In the context of the whole saga, Hayden is Anakin. Sure, you can understand that Shaw is supposed to be Anakin, but the fact of the matter is he never once looked like that in any of these films. Not to mention, continuity-wise, Shaw is far too old to be playing Anakin (he still works as the unmasked Vader because his injuries, the suit, and the dark side have made him more decrepit). You can say that it doesn’t make sense that the ghost would look like he did decades before he died, but I’d argue it makes as much sense as an imagined fantasy version of older him.
Now, the other thing people complain about is that the Hayden footage was a costume test, and it doesn’t fit. This is true, and it’s a little janky, but it’s not that bad. Here’s the thing though. The people saying Shaw’s acting is not being respected? That’s silly. Shaw’s acting is intact, in his scene with Hamill. Shaw’s ‘acting’ in the ghost scene was literally just George telling him to smile at the camera. That’s it. He had no idea the context, what was going on, or why he was smiling. So I’d say that’s only marginally better than a costume test.
Ultimately what it comes down to for me is that Anakin/Vader shouldn’t end up with a ghost at all at the end of the movie, so both versions are stupid to me, personally.
He didn’t look that old as ghost. If we consider the Prequels Canon, Anakin should be in the late 40s/50s, not young like Hayden Christensen.
About disrespecting actors, i take the opposite view. I believe all the actors of Darth Vader/Anakin Skywalker were disrespected. David Prowse, the original Vader was overdubbed, replaced by Shaw in RotJ and later ostracized by George Lucas. Sebastian Shaw who plays the unmasked Vader in RotJ is now removed in the final scene, and his face is covered up with CGI(removed eye brows, changed eye color). Jake Llyod was mobbed for playing the young Anakin in TPM. Hayden Christensen is hated for the performance that George wanted from him.