Vader was never a character that believed he was doing the right thing. He was a power-hungry monster. In ROTJ it’s clear he knows what he’s doing is wrong.
The most ideal version would be accepting that he’s become a monster but pretends he doesn’t care.
That’s kind of where I am with Vader. It should be depressing that he accepts his fate and keeps going back to the well of the dark side despite the pain it gives him. “It is too late for me, son,” should be the key line.
Giving this “addiction” interpretation more space in the PT would be welcome, as well as in spin-off materials. You can’t really insert it into ANH and ESB for pacing reasons (even though one can read it into Vader’s actions in ESB, finding a partner in addiction). Also, it makes Obi-Wan’s attitude towards Vader in ROTJ seem even more dismissive, which makes Luke’s triumph resonate even more.
I wouldn’t say this interpretation was intended at all (correct me if I’m wrong), but it fits.