I was being bored at work and decided to look at the main issue with mmo balancing.

 The most balanced mmo is based on a "rock paper scissors" system. The most basic rpg for that has just 3 classes. Tank, Healer, Dps.

 But the problem with this is, there are a lot of people out there with different tastes and interests. And having just 3 classes doesn't appeal to a huge audience anymore. The main reason for this is, because with the setup of a tank, healer, dps there is no room for solo play. A healer can't kill anything without dmg, the tank almost can't kill anything or will take hours to kill it and the dps can't take dmg.

 So game creators have to  make their classes being able to solo. This means that they have to break(adjust) the basic 3 classes. Giving a healer dmg and some tank power, a dps some tank power and recovery and a tank some dps and recovery. At the same time they have to make more then 3 classes to create a deeper and more varying gameplay for their players. 

I'm not sure which process their classes undergo, but it's obvious that in the end the rock paper scissors system is broken or not in game at all.

 The problem is since you have the 3 base archetypes, all the classes you make should fall under one of the 3. A lot of game makers do this, BUT they forget a main point. There are a lot of other criterias that they add to characters. Since the characters have to be able to solo, they add dmg to healers for example.

 BUT there is not just 1 type of dmg. There is Physical and Magical type. Unless you convert all dmg to be just dmg, and not 2 different types. You can not just make 3 classes for each basic archetype (healer, tank, dps) everytime you decide to add classes, but also split these for each type of dmg. 

This means, if you make a healer and tank that do physical dmg and a dps that does magic dmg. The balance is broken. And when you make a new class you have to make 3 and not just 1 to solve this. The 3 classes that you add will have to be a healer and tank that do magic dmg and a dps that does physical dmg.

 BUT, there is another problem that breaks this. The characters are not all close range or long range. So if you have the 3 base type characters for each type of dmg. BUT you have 1 ranged dps and the rest is close range. There still is no balance.

 And here is one of the main point I'm trying to make. If you want to keep class balance. You have to make as many classes as the types you split them in, and at the same time having exactly same ammount of counter classes.

 This means, that we now have a ranged type and a close range type, also magic and physical type of characters. To even this out you will have to have the 3 base classes for each type and have each type for each other type.

Here is how this would look like:

 Ragned physical: dps / healer / tank

Ranged magical: dps / healer / tank

Close range physical: dps / healer / tank

Closer range magical: dps / healer / tank

 As you can see you can easily calculate how many classes you need to keep the balance, depending on how many main criterias you add to a class. As it is here you will need at least 12 classes to keep the balance. (2 types of dmg x 2 types of classes x 3 the base classes)

 Now this is a very simple version, but these are the main types that all of nowdays mmorpgs have. To lower the ammount of classes you would need to change types. Making every class ranged or close range, would mean you can have 6 classes, and making them deal same type of dmg would lower it down to 3 classes.

 But since the games are undergoing an evolution and not a devolution, I would say that you would have to look in the other way. Which means you would have to keep the current named types, and actually add more of them. Types as: aoe and single dmg +2 types = (2x2x2)x3 = 24 classes. This would mean that you would have classes like: "ranged, physical, single target, healer" or "close range, magical, aoe, tank"

 And now that I mentioned the magical tank. This is another main point that I want to look at. Since most mmorpgs make a difference between magical and physical damage it brings another big issue with balance. In most games 70% of the monsters or more deals physical damage. Making it way more usefull to pump up your physical defence more then your magical defence. To make the class balance work right not only you will need to implement the 3 base classes to each type that you add to the game, but also make each type as usefull as the other one.

 This means that you would have to make the ammount of enemies of each type in the game world (almost) the same.

 For example when you implement a: "Man-eating Slug From Hell" which has 20000 physical attack and needs a physical tank. You would have to implement a: "Vegitarian Slug from Heaven" which has 20000 magical attack and needs a magic tank to take it on.

 Also you should make enemies that do both type of dmg. And have fields that have enemies that spawn in turns (when you kill a physical dmg enemy it spawns a magical one of the same strength when it respawns instead).

 Having this type of balance isn't enough yet though.

There is also the issue with overpowered or underpowered skills. This especially bothers players in pvp. Also one of the main reasons that lots of players tend to choose a certain class, not because they actually like it, but because the class seems or is imbalanced due to its skills. And eventually this leads to so called "nerfing" of the class. Changing classes leads to a lot of complains, and is something neither side is waiting for.

 This is why the skills have to be tought through a lot, and this is the reason you don't want to have too many classes. Because each class needs to have its individual type of skills, and every time that you add a skill to 1 class you have to add 1 skill of the same value to each of the other classes.

 And here is my vieuw at how to look at skills.

Each class should have a balance. Because you have 3 type of classes. You can put each skill under 1 type of character. But because each character has to be able to solo none of the characters is completely pure build.

 This leads to the fact that you will have to split each character in a point system or a % system.

A healer would be: 50% healing 20% tank 20% dmg dealer

A tank would be: 50% tank 20% healer 20% dmg dealer

A dps would be: 50% dmg dealer 20% tank 20% healer

 Each skill that you will be adding is worth a certain ammount of % for each type of class, or even multiple types. (This example is long, and I'm using just random numbers in it, to show how.)

 For example: "Divine Barrier Of Invincible Recovery" A skill that blocks 800 damage and heals you for 500 health points over a period of 10 seconds, with a casting time of 1 second, and with a cooldown of 1 minute, costs 250 mana.

 This skill, heals, but at the same time it helps tanking, but it does no dmg. Also its tanking value is higher then its healing value (absorb 800) (heal 500) And if we say that every 1000 health every 1 second  of damage, healing, or tanking is worth 1% And that every 10 mana cost gives 0,01% of cost back and every 10 seconds cooldown give another 0,05% back (all depending on how the combat system in the game is, and every developer should calculate their values depending on their combat system) this would mean that this skill is worth 800hp / 1000hp = 0,8% tanking 500hp / 10 / 1000hp = 0,05% healing. 60sec cooldown / 10 x 0,05 + 250 mana cost / 10 x 0,01 = 0,55% back. And since % wise this one gives 0,05/(0,8%+0,05%)x100=5,89% healing and that would be 0,032 points of healing back and the other 0,52 points to tanking. Then 0,8%-0,52% and 0,05%-0,032% Leaving the cost of tanking at 0,28% and the cost of healing at 0,023%

 And if you give this as the 1st skill to a tank, it would mean that he has: 49,72% tanking, 19,973% healing and 20% dps of skills left to be added.

 Now because it is an online game and you will always be developing it you can not make a character use up 100% of it's potential. So you should have its skills at 90% max at start.

 As you see it is important to look at every aspect of the skill 1st before you determine how much points it's worth in each area. Having a point skill for skills helps you, or even if you decide to let the players choose their own skills, limit to how strong each character gets, and since every one of them will have same maximum, and you actually make sure that you calculate every aspect of the skill to have the right ammount of points or % given to that skill.

 Also after you add such a skill in this case to the tank. You will need to be adding a skill that is worth exactly the same value to each of the other classes. Because adding something to 1 and willing to maintain balance, means you have to add something of the same value to every class.

 But even if you add something of the same value, you also have to make sure that every skill you add has the same kind of usefullness as the other one you added. Adding a 1 hit kill skill to a character and giving all others a healing skill that is worth same ammount of points and same cooldown, still doesn't keep it balanced. But making sure every class has skills that are worth exactly the same ammount in how usefull they are, and their effect is very important. My main point here is that if you add 1 skill to a class, you have to add skills of same usefulness to every other class.

 Then besides all this there is the issue with equipment. In some games (especially f2p) you can become extremely overpowered no matter how bad yor character is, as long as you can get this and that equips (in f2p games often with the help of cash shop). Which also means that looking for balance in an f2p game is looking for something impossible, as long as they keep adding items that actually affect gameplay to their cash shop.

 This is why I am looking at this as if there was no cash shop.

To start with You could make 2 type of equipment, an obvious best for pvp, and other pve equipment. The main complains about equips comes from the pvp side. This is why you can make equips that have bonuses that only count for pvp. And are way less effective in pve, and are gained by pvp. But most important of all, is that the equips are possible to be gained by everyone. The somewhat easy to get end game equips shouldn't be MUCH weaker then the hard to get ones, providing as few difference in gear as possible. The hard to get ones should still be worth getting though, or a lot of people would be dissapointed.

 I will end this for now as it is a huge wall of text already.

Hope ya enjoyed reading it if you actually made it this far.