Julifly,
You are oversimplifying a bit. Peak EGT cannot be found by feel, only by instrument. Leaning till roughness and then enriching, you could be LOP but anywhere else too. Running AT peak EGT (smooth engine) is better and cooler than 50°F ROP.
You can lean at any altitude. The full rich position is there to protect the engine at full power. A very rich mixture slows down combustion and lowers CHTs. A LOP mixture also lowers CHTs and is less stressful on the engine. In my airplane, running LOP (all the time except take-off and climb) saves enough fuel to pay for the engine overhaul at TBO. My engine is in perfectly good health according to the oil analysis.