I don't get why people are viewing map simplicity so negatively

At least what bothers me about this change is that Masteria provided more than just training, it provided a decent quest line and a world designed to go along with it. Simply put, I valued the ambient and the story tied to the area more than its usefulness as mere training maps, and it provided a change from endless grinding in flat maps (which seems to be the only thing people care about nowadays). You know, immersing yourself in the game and whatnot.

If on top of not having any kind of story, you rip out every other thing that defines modern gaming because "it's not useful", you might as well go play pacman. Or tetris.