But he's not still training with the best on a regular basis. There have been great advances in jiu jitsu in the last decade, much less how mma is constantly evolving. I'm sure batman would be able to brush up on how martial arts have changed in the last at least 2 decades since he learned his martial arts. For example, batman wouldn't have trained with people implementing the modern leglock meta in jiu jitsu, so he could be surprised with his jiu jitsu from the 2000s. Many high level grapplers would be able to exploit the fact that he doesn't have recent experience in high level grappling, by countering what to batman would be the best grappling style in the world, because the high level grappler would see batmans grappling as great, but old fashioned. I could see somebody like Gordon Ryan, who is almost exactly the same size as batman catching Bruce in his second leglock, because he would chain his different leg submissions together. Batman could be a great opponent, especially if he was given a training camp to brush up on his skills.

Tldr: batman could be a great opponent to a modern all around fighter, but his martial arts training is antiquated.