These clones are not reaching. He would blast them away with suiton jutsus or lightning wolf
Then that gives bee enough time to reach BM & laungh his bijuudamas, if kakashi doesn't snipe at the beginning of the match then he dies. Gaining distance is only so that bee won't get damaged by his own explosion, if he has to he'll shoot it regardless seeing as he can survive one. Alternately, he can whirlwind once the clones are out, thus giving him a safe distance.
Well if he does it, he can't exactly attack either and Kakashi is actually a better substitutioner than him. Sharingan will read the substitution handseals anyway unless he does that outside Sharingan's field of vision, so it's not helping him
The original isn't attacking, he's gaining as much distance as he can. Kakashi's superiority with bunshins doesn't change anything, there are more of killerbee & creating clones will only be a detriment to him. Plus these clones stick to kakashi so if he doesn't use a long ranged jutsu he gets sealed. He can possibly hide like a mole but using kamui to escape isn't happening, the clone will just come with him.
I didn't say he would spam Kamui on the Bijuudama. It's only in case he only send one. If it's multiple, he only need to dodge via hiding in the other dimension. And actually Kakashi do can spam Kamui. He used something like 8 Kamuis(including large objects) since he returned back from the battlefield including a off-panel fight with Black Zetsu and that occured after his fight against Obito(so tired)
If he hides in the dimension then he loses, bee will just wait him out in full BM & be ready to launch his tbbs. & I said show me kakashi spamming kamui
consecutively, I already know he spams it but he needs to take a break between uses still.
And that was tired Kakashi(after his battle against Obito)
A healthy sasuke still got eye strain from using susanoo + amaterasu. Kamui hurts kakashi, unless he can somehow tolerate the pain that comes with using it multiple times in a row then he can't.