There is a sorta 'best of both worlds' approach. Why not make at least some abilities questable BUT the ability is rare/ex. So no one profits and people still need to complete a step or two to fill out their action bar. I'd like to do quests to learn skills BUT I like learning some just for ranking too. A blend could be a good thing.

Example: I'm a rank 50 CON. One day the rank cap will be raised. I still learn Fire III when I hit the appropriate rank. But then maybe I have to do a 'Save the Elementals Quest' and for saving a fire elemental from impending doom, the Elemental is so thankful he teaches me Flare II. ...It could work hehehe.