I think the problem you're perceiving is that a class is complicated when played excellently and not that complicated when played averagely. That's good class design if you ask me. You are playing an online game, therefore there is huge variance in player skill. There NEEDS to be ways for players to go above and beyond and there needs to be content that can be done by those who can't perform to the highest of expectations. MOST players can pull out the minimal numbers required for their class in content and that's okay.

What I think you think the problem is is that the deviation from amazing and average or above average is noticeable, but by no means mandatory still unless you're in savage (Which is current end game content). You're comparing yourself to the best of players and assuming that makes you bad. That's not true. You are probably a good player... there are some who are just better and that's okay.

The only exception to this in my opinion is Black Mage. There's not many decent Black Mages and that's a shame. You're either blowing things up or resorting to your 2.0 rotation when things don't go well.