I once had a C172 that a previous owner had installed a MP gauge. That machine had a static RPM of about 2240.
Shock horror the MP was just over 29" on most days according to my instructors who first taught me the "rules" of operating an aircraft with constant speed propellers that engine should have been toast!! However that machine used to fly parachute and glider tow operations and was full throttle day in day out and did well over 3000 hours.
That was when I realised my instructors didn't have a clue
The BE76 is a classic in that the AFM has the climb power of full throttle and 2600 or 2700 RPM. However the instructors were told by the CFI that climb is 25/25 and that is what they taught. Even after I managed to demo them that if you fly it iaw the AFM the CHT would comfortably sit at 380 degrees. At 25/25 the CHT was just over 460.
I have never heard of anyone not having the confidence to run a fixed pitch aircraft at full throttle (without knowing it being oversquare!!!!!)