Yeah the whole point is that there is actually choice involved... More useful sub skills means more decision making in choosing your few slots.

The way the game is now it should just auto assign the cross class abilities because there are not more useful options than there are slots.

Yes people min max and if that's what you want, a build exactly like everyone else's, you'd be more than able to do so. I personally would like to see some form of customization between characters.