It's probably the myth about City boasting a bigger squad, which might have been true (or certainly nearer to the truth) in the Hughes/Mancini era, but has since seen been reduced to around 18 regulars plus youngsters and 3rd choice goalkeeper.
However, I suspect that United's latest defeat might tempt a few journalists into a more truthful comparison, especially as City don't have any unwanted peripheral squad members such a Lingard, Mata, Martial, Van De Beek, whose combined wage must be hemorrhaging their accounts.