Maybe he was always able to go pretty much all-out against Max without worrying about that, thanks to Max's invulnerability. I mean, otherwise the FBI description wouldn't make a big deal out of Max being able to survive a fight with him. Presumably lots of other supervillains fought hero-Tony and survived, but only because he was holding back.

We also know that Tony doesn't really become a much better fighter when he stops holding back. He's meaner, but as Survivor pointed out, he lacks skill.