Too much delay attributed to the ANSP means they get hit by penalties
Yes, but it i not the passengers who make the decision on the penalties is it? I will be the actual recorded delays attributable to the ANSP, so it still makes no odds.
As far as blaming CFMU rather than ATC for the slot is rather difficult. The avergare layperson will know what Air Traffic Control is but not Central Flow Management Unit, and the distinction to them will be very slight, so I wuld suggest that a PA explaining who CFMU are and that they are the ones who have issued the slot will become far to rambling and technical.
I am sure that ATC'ers are quite rightly proud of what they do, but occaisionally we all have to take one on the chin for the "cause". The ones who really have to take one on the chin are the cabin crew. No matter how well you explain the reason for the delay the pax always give then cabin crew s**t for it.