I think there has always been a reluctance to Lean probably from training days when instructors were scared students might stop the engine and scare themselves or overleen and damage it!
The POH of our Archer specifically states that the 'normally' aspirated O360 should be operated full rich at anything below 5,000', so that's what we teach the students. I've seen this debate over 'lean/don't lean' for the past 35 years and I'm none the wiser (for carbureted engines).
HOWEVER, for injected engines, I've always leaned at any altitude (against the EGT) and with the Continental, for instance, in the Reims Rocket, on the ground, too. Friends with a Beech 33 have a clever gismo which enables them to operate 'lean of peak'. The oil after 50 hours looks as fresh as when it was put in. The engine is 'on condition' at nearly 3,000 hours and seems in fantastic condition.
TOO