AEDU is awful system. Limits the progression, homogenizes the classes, AS for mmos having cooldowns, UO had no cooldown and Mu Online too. Mu Legends in other hands, is a wow clone,

As for spell slots being inspired by literature, see TV tropes, they mention TONS of novels with it https://tvtropes.org/pmwiki/pmwiki.php/Main/VancianMagic

Not all fantastic literature should be based on Tolkien, D&D took inspiration on Tolkien but also took inspiration on many other things and i posted a interview with 4e devs talking about how 4e is inspired by mmos.

As for 5e being shallow, i agree that 5e is not perfect. The game is too rigged in favor of PCs, the mechanics are too dumbed down, but by other hands, they reduced the high level power creep and made easier and funnier to DM.