I'm willing to give back VI as an instance of locked classes. Technically if you build Locke up with a speed-boosting esper, you're essentially stuck with that decision. No swapping back and forth between high speed or high strength.
Even without VI, the majority is still in favor of switching jobs around on a whim. I think some of the Tactics games and maybe FFIII had a stat growth feature that would apply on level-up (so MNK characters tended to have higher HP even if they switched to WHM later on). But that's still only a small limitation to job/ability swapping.