@Jabberwok:
I'd guess it's somewhere in the realm of both. My personal theory is that Katakuri relies too much on his Foresight and is generally kind of lax when he doesn't notice an imminent threat.
My thinking is that Conqueror's Haki might have the effect of disrupting the other two kinds of Haki if it's strong enough. It would give it a more relevant effect than visual flash and mook remove, and it underlines the special qualities of those ambitious enough to manifest it. Katakuri with Foresight is almost invincible, but without it there's a chance.
I've been hoping for a while to see Conqueror Haki applied more directly, against a stronger opponent. We've seen it can cause physical damage before, so maybe it involves other stuff as well. Disrupting concentration or predictive abilities as you say.
On the other hand, there's awakening, and in front of him Luffy has a clear example of what he could do if he had more control over his devil fruit.
Then there's G4 and more possible forms. Maybe he has a form more oriented against fast opponents. Frankly, it would be weird if Luffy didn't consider something like that. But then why not use it against Dofla? Unless he only perfected it after Dressrosa.
Not really sure what kind of weakness Luffy could exploit inside of Mirror World. One thing that comes to mind are mirrors themselves. Perhaps he could find a way to gain an edge over Katakuri with reflections. Not sure how, at this point.
Doubt it's possible without any power up. It doesn't even have to be a big one, because it should be a pretty close win, as it always is when Luffy faces someone with superior skills.