I think there's always going to be people trying to be lazy about it. You can't boot them cause the system wouldn't make sense. The game identifies when someone is afk, but if they move around then they will be fine. Based on kills? That may also be unfair. What if someone has a Gjallarhorn for the boss while the other takes care of the adds? So since that's the strategy they choose then one guy suffers because he uses Gjallarhorn for a single enemy, the boss. You want a real solution? Get some friends to run with.