Simply because you don't like Minato doesn't in any way lower his reflexes or upgrade Obito's. Deal with it, Obito is very sluggish. Not because the Kamui is sluggish like you say.
And you say that Minato was unable to land a proper hit till then? Tell me, when did they infact fight before that time? Oh, right, Obito fought, but Minato did not. He had only seen Obito's intangibility once before. In-order to avoid a mistake, Minato went into battle with Obito without pre-conceptions once more, where the rope thing happened. Minato used that tryout to assess Obito's skills and pawned him with the next move.
He's got a sharingan, can see Minato coming at him in slow motion, can see Minato throwing a kunai to his head in slow motion, and still can't react to Minato's rasengan. Yeah, best reflexes in NV. And btw, Minato outdid B and A together, multiple times, after that incident. Why're you forgetting that?