I think a Batman who can survive explosions to the face and wiping out in a wing suit and then climbing up to the top of the same tower he jumped off ten minutes later will have no problem hanging with the Justice League.
Plus, The Batman wasn’t *so* good that I need them to keep it “grounded.” It was a fun authentic Batman, but it was also a film with like… 6 acts. I love Matt Reeves, but this film was Bloat City. The property would be improved with Gunn’s input. Say what you will about Gunn’s aesthetic/humor, but he knows how to structure a film or series perfectly.