Soi Fon's one of the captains he's interacted with the least- I think he saw her at the execution, then just now, and that's it. So she'll have some respect for what he's done but insists on manners.
And she is jealous of him hogging Yoruichi 🙂
You're right on all counts but Hachigen needing her to beat Barragan. Their team move didn't kill him and it turns out Hachigen had the one technique that Barragan couldn't defend against.But yeah, he could have done that on his own.
He wouldn't likely have known about the weakness without the prior attempts and info gleaned, would he?