Yeah, honestly the idea that you'd ever switch back to your class after level 30 is kinda silly when you consider the fact that even if you are missing some kind of "diversity" ability (Which almost always means self-healing because you're soloing), you can actually gain that by calling your Companion Chocobo.

Almost all the customization in this game is illusionary and only there to make you think your choices affect your character. If I swapped back to Archer from by Bard I'd have 0 new DPS abilities. I could set maybe a couple defensive moves and if I tried to set Cure I'd never use it because it heals for something like 60 HP.

It's crazy to put your 30 stat points into anything other than your primary stat. A BRD that specs all Piety for instance, will be laughed out of a room. It's been found that STR scales very, very poorly defensively (Something along the lines of 30 STR for +1% parry reduction) so that MRD/WARs picking STR over VIT will only be better for speed runs because of more damage, etc.

Still, I wouldn't say that the OP's suggestion is a bad one, because they could fix these problems pretty easily with a bit of work. If you made it so that, say, Archer has higher MND than Bard and gave it AF that increases both DEX and MND, it would actually make some sort of sense to be self-curing with magic.