Tactful ways to inform people that they're playing badly?

[SerLuke]

Looking at it from the wrong angle. How much time will be wasted by the noob in the next several hundred runs they join because everyone refuses to do anything about it?

You are missing the point, you are trying to make it look like you are doing a noble thing by kicking someone from a casual dungeon run because they don’t meet your standards in order to make a run go a couple minutes faster or leaving and giving oneself a 30 minute penalty without saying anything because they think it will magically make someone play better in the long term.

Let’s be honest here shall we? You don’t care if that player improves or not you just want to have quick, fast runs, you are trying to make yourself look noble in a vain attempt to disguise your own selfishness you would rather all players that don’t meet your standards quit if they don’t improve in a timeframe that is acceptable to you.