While I agree it's a lacking reward for the storyline, doing story missions isn't really about the reward, but going through the story. FFXI is plenty enthralling w/o doing any storyline, but if you want a story, that's what missions are for.
CoP was so difficult (originally) that the rewards needed to be equally epic, to give incentive when your spirits were down.
The end reward isn't incentive others redo the missions with you, so that side isn't affected.