I used M (for manual) mode for too many years starting in 1962 with my first serious camera (Olympus 35 mm range finder).
The focus was manual, the light meter was manual, etc.
Then with a Pentax S, the focus was still manual, the light meter was manual, and the diaphragm stop-down was manual (so was the film advance lever).
The hell with manual - I've had enough of it. I also drive a six speed automatic car.
But I do understand the point of using M when lighting conditions are stable, but the subject can change (sports venues). And damn it, my favourite lens is manual focus (TSE24II).
PS - I agree with "guntoter" - the metering in Av can be variable.