Anakin WAS redeemed as an old man, therefore, he should be an old looking force ghost…for lack of a better way of putting it.
Every time these discussions come up the most simple answer is always ignored; Hayden was put in because the audience can actually identify with Hayden’s Anakin. Shaw’s Anakin is never once seen at any point until the final minutes of Return of the Jedi and Hayden’s Anakin has two entire movies and almost five hours of screen time dedicated to him. If you put Return of the Jedi in the context of the six film saga then Shaw’s Anakin is visually out of place, it’s really that simple.
There are thematic arguments in defense of both sides but the simplest answer is just audience familiarity. I personally find the hate on Hayden’s Ghost Anakin vs. the Palpatine recast extremely hypocritical and screams of anger filled double standards; trying to rationalize the double standard just digs the hole deeper.
I personally prefer Hayden’s Ghost Anakin even though I grew up with Shaw’s Ghost Anakin, but as with every SE/Theatrical debate I think both sides would be perfectly happy if both versions of the films were freely available to the public, which should be the case anyway.