You very poorly understood what I said.
Mihawk was able to low diff Zoro in East Blue by using just enough of his strength to create a certain gap between them. I believe Mihawk can recreate that gap, even while using his knife, simply by adjusting the effort he uses to accommodate Zoro's growth in strength. Which means, using Haki, dodging, blocking attacks, etc.
He can infuse Haki into the knife so Zoro can't cut it. He can infuse Haki through his body to tank Zoro's attacks. He can use his speed to dodge them. He can use his speed to get in close and pierce Zoro's Haki with his own, stabbing him in the throat.
If Mihawk is at his peak at level 100, then Zoro will be able to beat him if he reaches that level or surpasses it. For now, he's nowhere near it, so he'll still be low diffed if Mihawk puts in enough effort.