Interesting point, KKOB.
I, like you, have spent 30+ years in the transport industry (BA, Japanese Airlines, Phoenix (US Airline) - intermingled with 7 years in the Police when I fancied a change).
It's not the reason for delay that I consider so much as the way I'm treated during the delay.
I cannot think of any situation when an airline has offered "incompetence" as a reason for delay. Neither, I am sure, can you.
Absolute proof of incompetence doesn't exist.
Never has, never will.