How could DDs already be less unique? Other than a couple of class-specific abilities, everyone could already use everything, and generally the good WSs for one class stay useful on other classes (Bloodletter, Skull Sunder, etc.).
And overall, MRD and LNC played a lot alike, ARC and GLA still going to play differently, and the only one that got its combat style made more generic is PUG.
Mages will actually have to have some skill rather than just put on a scepter and spam Sacrifice.
Yoshi specifically said there would be a period when it felt like SP slowed down before all the changes through 1.20 were finished, so yes, for a little while leveling new jobs will be suckier. On the other hand, there are going to be more things to do besides just level new jobs.
Battle speed is the only one I'm really worried about, because fast & frantic is a lot more fun than slow & deliberate.