My reference to 'big arsed radials' was only for magneto checks...typical mag checks as taught by most flying schools in C152s etc indicate a lot less about the condition of the system than you'd think. That is the reason I do my mag checks in cruise. I learned that from talking to Deakin about 5 years ago.
I agree about RPM...unless you are talking MP/RPM
AND Mixture as a whole you really are not discussing the complete picture...having said that the only engine control that can adjust power from 0%-100% is the mixture control.
The throttle position and prop rpm control the air side of the fuel/air ratio and the mixture controls the fuel side with a slight overlap in the prop control because prop rpm also governs engine driven fuel pump rpm...I can lean or enrichen the mixture within a small range just with prop rpm
The mixture control is
the most important engine control and the least well understood/least well taught.