There needs to be a middle of the road in my opinion. One or two of the top loot is rolled off, and a couple of the top contributors get a guaranteed piece.

You can't tell me it's fun to work your butt and lose it to someone that showed up on the last mob because they lucked out with a huge roll?

I don't think set rewards will necessarily kill participation either. People tend to stick around for more than one run from my experience in WAR. If you're too you late to get meaningful contribution, then the quest is probably decently far along the chain. You help out, the quest gets finished, and it resets for another go faster than waiting for it to reset on its own. I think you might be overestimating how selfish people are honestly. Loot is nice, but playing the game and having fun is better.