Getting abilities or power from duties has been brought up on the forums before and I can appreciate that some people prefer to chase power instead of mounts. Yoshi-P has even expressed that he understands people who chase power in video games. I think it obviously goes back to that they want to make the game work for the most casual of casual players.

I think they could do it an alternative way by making it drop things that adjust playstyle or add optional utility and then make that utility or playstyle stronger as item levels grow.

My guess is they won't do this though since they will likely just do something resembling Skill Trees and Talents, the Blue Mage system, the cross-class system or phantom jobs (which if you think about it is a good way to test what works before adjusting jobs).