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http://rampantgames.com/blog/?p=3723
A detailed look at the trade-offs - pros and cons - of class-based systems vs. skill-based systems. Simplicity for new players, restricting or balancing content, power fantasy, imbalance and unviable builds, and more.
http://rampantgames.com/blog/?p=3720
A brief definition of and look at games that use classes with fixed skills, free selection of skills, and hybrid options, with some of the pros and cons of each approach .
https://kotaku.com/how-to-balance-an-rpg-1625516832
single-player RPG JRPG balance classes
Why and how to design your single-player RPG character classes so that they're mechanically interesting. You want players to make interesting choices through trade-offs. Make big differences, play-test, and use spreadsheets to balance.
https://gamedev.stackexchange.com/questions/83251/why-are-character-classes-used-in-game-design
RPG JRPG roguelike MOBA balance classes
Benefits of adding classes instead of using a class-less system in your game. They make it easier to balance, they help new players, they can provide class-specific quests or story plot points, and more.