I am usually playing healer, or tank, and I can usually tell for a fact when each role is 'underperforming' - and it's quite often. I find it hard to believe that people aren't seeing it. It's quite easy to tell when player(s) are either performing adequately or not, from how long it's taking to kill groups of adds, how much damage a tank is taking, how well aggro is managed, interrupts used, aoes , esuna being used, vuln stacks, etc. etc.. Even more so if you regularly play a class and know the regular combos for situations.