I think Van was capping with his Batman take primarily because of 3 reasons:

1. Batman lacks prep time, so he will be unfamiliar with lightsabers and the concept of the force. Against any lesser opponent, Batman might be able to adapt, but Obi is an ELITE Master Jedi.

2. Obi-Wan is a MASTER of the Defensive form Soresu, so I don't think Batman's martial arts training is that much of an advantage over Kenobi.

3. While Cad Bane gave Kenobi the business in the Clone Wars series, and Jango in Episode 2, there are some key differences when Assessing Kenobi'd fighting prowess: 1. Bane and Jango are prepped to fight Jedi specifically, while Batman lacks that knowledge. 2. Kenobi in Episode 2, when he faced Jango, was dramatically weaker than Revenge of the Sith Kenobi.