Comparing Zoro vs Mihawk to Ace's death is a ridiculous comparison.
I wasnt the person who did it.
Remember Luffy vs Crocodile? Remember how Crocodile beat Luffy multiple times, but he still got up to keep on fighting? That is an appropriate comparison to Zoro vs Mihawk. Just like Zoro, Luffy lost to someone who was much stronger than him. The only difference is that while losing literally broke zoro, Luffy didn't care.
And? No amount of willpower wouldve made Zoro win against Mihawk. Exactly like no amount of willpower wouldve made Luffy win against Aokiji or Kizaru when he met them.
The difference is in their attitudes towards their losses - Zoro losing to Mihawk is his worldview coming crashing down on him, that he's faaar away from his dream and as Mihawk said, he's a frog in the pond. Unlike Luffy, Zoro's ambition is based on strength and losing is a bigger deal to him than to Luffy. You can literally see how Luffy and Zoro took their losses against Ace/Sabo & Kuina respectively when they were kids.
This whole topic was started when you used Zoro crying after losing to Mihawk as an example of him having weaker will, which is wrong when you ignore the context behind that scene.
Zoro also fights combatants stronger than him - King, Mr. 1 and Kaku. The only difference is that he cannot lose whatsoever thanks to his promise and he grows within the fight to win.