While I've thought of this myself as I consider buying myth gear (should I *really* buy the PLD gear or will I like DRG more once I've leveled it?), I then think, well what the heck will I DO with that gear anyway, just stand around looking cool? Speedrunning more dungeons to the point of bland oblivion?

I think more important than gearing up multiple classes is offering far more challenging, satisfying content for level 50. Fights that insist on excellent mechanics and are more forgiving to gear, so you would be fine with your AK gear and any old weapon. I for one stopped even trying to get AF2 because it requires hours and hours of extremely boring and unchallenging gameplay.