- On loot hewers
Institute a DKP system. Problem solved.
- On mediocre DPS
Tough call. It's hard to force people to play a certain way. At some point I would think it would feel like '...Why am I even playing? My guild is forcing my spec and rotation. I might as well be a bot.' That would want to make me quit for sure.
IMO, all you can really do is educate. It's up to the horse to drink from that water.
Hope this helps