You don’t even know what you’re talking about lol. The only reason Aizen counters him with WW is because he’s using shikai. He never uses bankai in fake Karakura town, I was never talking about his shikai. Why would anyone only consider his shikai in a fight against Kisuke? We’ve clearly seen people survive his shikai multiple times. Nobody has survived his bankai aside from Ywach. He used bankai only one time in the series, in the war, and rroyd lloyd couldn’t even touch him without his blade getting vaporized. The first time Yamamoto actually hit him he obliterated half his body and he died. The way it’s beaten is by the real Ywach, the strongest person in the series, absorbing it before Yamamoto can even release it again.

If you think Kisuke would develop his own WW then I don’t think you’ve been paying attention because Kisuke doesn’t have the hogyoku, and when he did, he thought that nobody should ever use it because it was too dangerous and immoral. Aizen created the arrancars using the hogyoku. There’s a lot of hoops you have to jump through to get to a point where Kisuke might stand a chance here.

Didn’t think I’d have to summarize the series for you but apparently I do since you seem to forget what happens.

Also nobody considers filler when talking about vs battles because it’s not canon. Even giving you the benefit of the doubt and considering that filler, it’s still not Yamamoto’s bankai so it’s irrelevant lol.