A set bonus? You can't get the full benefit of the gear unless you invest several slots into it? Trying to keep people from dipping one point into another groups gear might be impossible outside of arbitrary restrictions. You could re-spin things to be a positive. Maybe the gear doesn't raise your threat, but gives you more DPS the more aggro you have? Now it's not a penalty, but a buff. Still won't see it in a raid though. Messing up small group play would be a problem. Though I don't think you can make gear that is good for group and solo without it also being good in raids that seems like a 1+2=0 problem. Though what pops up has a lot to do with the encounters. You can pick and choose what aspects are included in the quest content. EDIT: Actually the ability to control what aspects show up in what content really helps balance things out. Like if raid monsters didn't critical, but solo monsters did. Then any crit resistance would be a stat useful in one group but not the other. It's arbitrary , but not too arbitrary. Balance is always tricky. Being able to customize your gear throws all kinds of wrenches in the system. I have no idea how you whould fix that or if you would want to. Maybe it's good to have some overlap?