>says he won't hold back
>wasn't even trying
Mihawk with a random swing aimed at Luffy cut the giant frozen wave apart that was larger than Marineford. He did that only once.
The next slashes he threw at Luffy, he did not even put enough force into them to kill or knock out somebody like Mr.1 straight away.
You may not like reality, but either Mihawk did "lie" and held WAY the fuck back after that one move to not erase Luffy from existence, or he secretly ate the "random random" fruit and every attack he dishes out has a random attack potency.
Personally? Think the first one is more likely.