Yeah but that's why "homogenization" isn't a single thing. As explained to you before. There are lot sof types of homogenization, and painting them universally as bad or to-be-avoided is not a good approach, too. It's not a binary system. It's a scale, and every design in every MMO falls somewhere onto it.
Too little homogenization, and balance is entirely impossible, not even close-to-balanced. This might be acceptable of course (depending on game) but most gamers nowadays expect some level of balance. This is sometimes intentionally done however in single-player games, because usually there we want classes to feel as diverse as possible.
Too much homogenization, and your design space collapses, it doesn't feel like you have, say, 20 options how to play, more like 4-5. The most common variant of this is that only your role matters any more, not your actual class. Melees are mostly there for example, tanks and healers are. PRanged and Casters mostly avoid this fate in FFXIV, at least so far. Might again be warranted, depending on your game. In games such as Counter Strike you want near-full homogenization, to keep the playing field as even as possible. In most MMORPGs you don't want tooooo much, because then people get bored as swapping to other classes adds little meaningful variety to their gameplay.