I wonder what the effect would be if there were content with individual mechanical consequences for low DPS. Fights where DPS below a certain threshold get knocked around and/or called out by the boss, some kind of mechanic that makes it clear Joe Schmoe needs to work a bit harder. Make the accountability visible, direct, instead of just a vague lack of stuff dying or phases not ending fast enough, without making it an explicit number. Wouldn't have to be every fight, either. Just a roadblock here and there that makes people have to figure it out so they reach a minimum capability threshold.