I think the hallway scene was a mistake. It’s clear it was intended to be this gratuitous fan service that people would get excited watching, which is rather tone-deaf given the sad deaths of the main characters that occurred just a minute before. It reflects a lack of confidence in the new characters by Lucasfilm, who must have thought that audiences wouldn’t be sufficiently emotional about Jyn and Cassian’s deaths, so they felt the need to give the ending more “oomph” by adding the hallway scene and pumping up the audience right before the credits rolled.

The scene reduces Vader to a silent, hack-and-slash murder machine, which isn’t at all what Vader was in the OT. And I agree with that Reddit user that George never intended for villains like Vader or Palpatine to be “cool.” At his core, Vader is a pitiable character. We’re not supposed to think of him as a badass, or get excited at seeing him commit evil acts, but that’s clearly what Rogue One wanted.

And of course, the hallway scene, and Leia’s presence at the Battle, are the two main reasons why the ending doesn’t line up well with ANH.