Kuma sent a Pacifista flying with one blow. And Sabo may know about Kuma, but that doesn't mean he'll win. Kuma doesn't need Haki when you have the ability to send anything flying while nullifying the effects it has.
I couldn't care less how you feel about the logic. It's not mine, it's Oda's. Was I the one who showed Kuma with the ability to deflect non-tangible/solid things? No, it was Oda. Was I the one who showed Kuma able to nullify the effects of what touched his paws? No, that was Oda.
Impact doesn't matter. Kuma repelled things with no tangible form, he was able to repel the air. Striking fire would create the same impact as striking air, so repelling Sabo's Logia form would be no issue. Maybe if Sabo disperses into fire and moves around his hand, that could work, but if Kuma makes contact with Sabo even once, Sabo is gone.
Who says he couldn't deflect the Hell Wink? That was Kuma with the mind of a Pacifista, Kuma with his own mind would have handled it a different way because the minds are different.
Close ranged fighters are horrible against Kuma. Unless your significantly faster than him, he's gonna send you flying the second you get close, and Sabo hasn't shown that speed.