Champions Online is open with its missions, that are open

Glad to see them doing away with the terrible roll system WAR had. Work your bum off only to lose to someone who just arrived because you rolled 2, and they rolled 900. Terrible.

Do the most, get the most, but everyone still gets loot.

I wonder if there will be an open mission in Sakura Park.

The roll system in WoW is what I would consider a necessary evil.
It's clear that everybody that participates in Public Quests are there for the loot.
However if said person arrives much later then the group that started the Public Quest, there is no incentive to actually participate in it since they are guaranteed shoddy loot.

With nobody but the initial players participating it's a good chance the PQ won't even be completed at all and thus ultimately nobody get the loot.

The random roll is to encourage people to actually participate in the PQ which is the most important factor and loot secondary to that.

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.