I can show you panels of Lucci clashing with G5 (with hardening) and pushing back like equals.
It's irrelevant, though. Luffy could have gone G4 against Lucci just like he could have used aCoC on his early snakeman punches. He chose to use a powerup with equal drawbacks against both opponents.
If you do want to use that line of arguing, though, I'll just answer with "He didn't even dare go G4 against Lucci".