Are you saying it takes longer to lean LOP than it does ROP? Or are you suggesting to skip leaning and leave the mixture full rich the entire flight?
It doesn't take that long to get into a "close enough" LOP setting, especially if you know your plane and set the power low. For example if I were told to briefly level off and demonstrate some sort of maneuver, I could level off, pull RPM back to 2400, pull mixture back to 8gph and good enough. Is it 20LOP or 80LOP? If you are doing it briefly, who cares? The engine is cool and you're not wasting fuel. Or coming into a hold, pull throttle back to 20" and RPM 2100, lean below 6gph and leave it till there's time to fine tune it.
If you know how to manage your engine while flying VFR, quickly setting it at a ballpark LOP setting is EASY and quick.