Dual Spec OPENS UP THE CLASSES.
It doesn’t homogenize them. Dual Spec allows players to play more aspects of the game, and to play more of their classes without being hindered by a respec cost.
FF14 classes all play nearly identically, I’ve watched enough of the game to see that. FF14 is an awful game. If you really like it so much, go play it instead of paying to post on the forums of a game you dislike.