I didn't have a problem with the fight itself. They made a point of saying that Superman could destroy him in a second if he wanted to. This was the first time Supes had experienced Kryptonite so it caught him off guard. Basically anyone can defeat Superman with Kryptonite. So it doesn't make Batman special that he was able to beat him with it. Yeah Bruce you beat him with Kryptonite, anyone could do that.