The game has been laggier than usual on my end since U5, and I'd be willing to bet it is because of the check for guild renown after every monster dies. Even if this is not causing lag, I would stil be for removing the renown per kill system.

I particularly dislike that it is automatic. It adds no challenge and requires no effort on the part of the player. Except for possibly one or two good monster farming spots, noone in their right mind farms monsters for renown. Chests and end rewards are just so much more productive. To put it another way, the devs long ago decided that it was a bad idea to give us xp/kill as in other MMOs, and yet now we get the equivalent of guild xp/kill. Why?

I think it makes more sense that you get famous for accomplishing the hard part of a quest (boss fights, optionals), not the easy trash mobs that are barely slowing you down.

To compensate for the loss of renown from monster drops, simply increase the drop rate in chests, or have the game give each character a chunk of renown at the end of the quest based on either quest difficulty level, or some monster killing formula like:
Total kills x renown chance = renown award.