Retail feels like it only has 3 different classes. Those three archetypes are then split into the playable classes and given different aesthetics. This is the basis for WoW class design.
Warrior - (Warrior, Death Knight, Demon Hunter, Paladin)
Rogue - (Rogue, Hunter, Monk, Enh Shaman, Feral Druid)
Mage - (Mage, Warlock, Priest, Resto/Balance Druid, Ele/Resto Shaman)
And so on…
Game designers throw a lot of things at the player to alleviate/hide this problem such as different aesthetics, maybe some class lore, resource mechanics, specializations, items, the progression/regression cycle, whatever. That’s all well and good, I mean there’s only so much you can do if you want to keep the game balanced and relatively casual gamer friendly.
I think a lot of the people who insist that the classic way is best are probably players who long for a time where MMOs were different. Before WoW changed the game, the differences between classes in your typical MMO were stark.
You could play a Warrior, everything about your character abilities from the ground up screamed Warrior. You were slow, clunky, but you had a ton of health and you swung a giant axe. You knew exactly where your place was on the battlefield and you knew if you moved from that place you’d be punished. Additionally, MMO players just kind of accepted that certain class archetypes beat others. Rogue > Mage > Warrior > Rogue. The cycle of life.
Early MMOs were great at making classes feel distinct, but there was a perception amongst players even then that class balance was a serious game breaking issue. Balance whining, you see, was pervasive in the community from day 1. The Blizzard approach started with introducing the global 1 second cd and building out three class archetypes from there, probably hoping it would make balancing the game as easy as 1, 2, 3 and assure that there was no “rock paper scissors” going on. Of course, over time we’ve learned that even with that system it’s still incredibly difficult to pull off when you want your game to be balanced around every different type of pve and pvp at the same time.