We saw how Hawkins power had increased with the straw man being a fair more powerful and intimidating version of the strawman he used against Kizaru(with the strawman post time skip actually giving Zoro trouble in terms of strength). We also see how effective his blade is in combat also.
Also, Law is just that good. I don't get the idea that he wasn't taking out Hawkins lives, because he obviously was, otherwise there would have been literally no point to attacking Hawkins henchmen(which were still alive) before aiming for him during their first encounter.
Not to mention, this was used as a sign that Hawkins would be getting ahead of himself if he fought Law again, and was only confirmed in the latest chapter.