Michael Keaton being virtually immobile in the Batsuit is completely, 100 percent authentic to the original movies. He could never move worth a damn in that thing, which is one of the key reasons I've always disliked that costume.
I distinctly remember Keaton talking about that issue back in the day in an interview. It led to his Batman move in a certain stiff way, i.e. he wanted to look in another direction and he had to move his entire torso. Ha hated it and was also part of the reason why he didn't do more Batman movies.
Now i wonder if they'll de-age him if he appears outside of the costume, right now it looks like he's present age Keaton but unless they go with grandpa Bruce Wayne they might use the tech.
I really did the idea behind The Flash now being the swan song of the Snyderverse, anyone know how much they changed to make it the bookend movie?