@Bele It's there to fix an exploit where you could get more stats per points spent, and unfortunately the way the game is coded means a fix would be too time consuming.
rawheadre you can get any loot at any damage in non-tiered raids, hitting too hard will increase the epics but reduce the commons, tiered raids have tiers, at each one you get more loot, they have a minimum tier required to get epics. Check the wiki/forums/script to know about the tiers of specific raids.