Link doesn't work. But I don't know how some other completely different character losing with it against a completely different opponent means it won't be useful against any opponent. I don't think it makes a huge difference, but it should make precise timing easier, such as striking at the "perfect" moment when Lemillion is vulnerable to harm.
Yes. This is why I mentioned after taking a beating for a while, he will come to learn Mirio's style. Not instantly know how he fights. He has the durability, endurance, stamina, and regeneration to last long enough to start understanding methinks.
This seems like something distinct from what I described. Izuku predicted where Mirio would pop up, and struck in advance (and failed). I'm not suggesting he does that, but rather wait until Mirio's fist is within an inch of striking Kaneki (Which he should be able to time due to his increased perception of time), and then strike him with his Kagune then. He may be hit himself, but that won't matter since it allows Kaneki to land a devastating single attack. Which is really all he needs. Deku didn't wait for Mirio to get in close for a strike like I suggested.
I don't think Kaneki wins this due to each of these individual traits, but the culmination of all of them. The stamina to persist for a long time, his ability to learn and predict Mirio, his enhanced perception of time allowing for precision timing and judgement, and his Kagune which can make precise movements and adjustments and be ejected from Kaneki's body at any moment. Plus his general combat intelligence.
If Kaneki didn't have the endurance to last, I would give it to Mirio, but all Kaneki needs is a single strike and he's won. From there he can just play keep away, and pressure Mirio to take riskier moves as he bleeds out and slowly succumbs to his injury. Which would only open up more wiggle room for Kaneki to land more strikes (Not that he'd need to, but it would accelerate his win).