The thing that really worries me about the idea of lowering affinity is that there is a very strong possibility that a lot of skills will become completely useless to a lot of classes. This would take out a lot of the customization that the game has right now and would really hurt the games appeal.

I think lowering affinity across the board isn't the best solution to this issue. I think a better solution is something of a sub-job like system. Instead of drastically lowering the affinity of all the classes to other classes, make it so you can choose two classes that don't lose as much affinity as the others.

You're primary sub-class has around 80% - 70% affinity, and your secondary sub-class has 60% affinity. The other classes have 40% affinity. This would fix the issue of being able to use all skills to their fullest as any class, while still keeping the customization that we have now and possibly even boosting the uniqueness of your class.

For example, let's say you want to have something of a melee/magic hybrid, something like a Dark Knight. So you start out as a Marauder, then you make your primary sub-class Thaumaturge, and your secondary sub-class Pugilist. The Thaumaturge spells would function at 80% to 70% potency, and the Pugilist skills would function at 60% potency. All the other classes (Gladiator, Archer, Lancer, and Conjurer) would function at 40% potency.

I think this would be the best solution because it wouldn't be as restrictive as the FFXI sub-job system, wouldn't be as overpowered as the system we have now, and would let people play the way they want to play.