I've always said that I think they should re-work skill progression entirely. If I sound like a broken record, i apologize!

For me:
1) By first dungeon (so level 16ish) your basic 1v1 and AoE rotations should be available. For examples: PLD, Halone and the 2 step AOE; Samurai the Gekko combo and Mangetsu Combo
2) By 50, you have all skills, in full.
3) Post 50, the skill bar related stuff. Again for PLD we're talking things like shelltron or the proc-abilities; for Sam, the Kenki gauge stuff

With new expansions I would rather they not add new abilities, but maybe expand upon current ones (lower the cooldown time, make more interesting choices with resources or just make the entire combat speed faster by reducing recast times.)

THEN, for the OP's original idea, YES! There should be some kind of area where you can practice avoiding mechanics or your rotation in a "live fire" situation...but it really irks me when they re-do the whole rotation unnaturally.

..like Samurai feels pretty smooth from 1 to 80; what you do at 50 isn't that different from 80. Blackmage however you have to re-learn your rotation at several intervals as it becomes wildly different depending on what you have access to.