I think it's interesting that so many people say there should be a reward for getting all classes to 50. As far as I'm aware, there already is one - diversity. You get to pick and choose and adapt your group to the fight. A group with many classes leveled is already considerably more dynamic than a group with very few and therefore are already more powerful in one sense.

I don't think that on top of that you should also put others who can't invest the same kind of time to shame on one equal leveled class. Not everyone has the kind of time to make their character awesome, but we should at least be able to level one class to cap and feel somewhat competitive on that one class, just as you could in XI. The armory system turns that idea on its arse. You don't have to even be at level cap to realize that the higher rank skills on other classes will give you a massive advantage.

I also just think it's pretty silly that the strength of your class would depend far more heavily on your rank in other classes you may not even want to play. How does that make sense? In order to play GLA well you should spend three times as long on other classes to get their skills. It's basically like the subjob system turned inside out and the subjob is now your main.