Marvel have to make "sliding timeline" decisions regarding their characters, including the Fantastic Four or the X-Men who are not possibly as old now in present day comics as their original comics would allow. The modern comics I remember where Punisher fought in Vietnam might have been MAX and not day-to-day continuity, and he definitely looked older accordingly compared to a clean face Frank. But I feel his story of family loss, and going from one war to fighting another, that kind of stuff, might not need to tie him to Vietnam exclusively when war is horrible in any decade and bad things can happen wherever you are.
But in Magneto's case, he's probably with Captain America as one of the characters most associated with World War II, which includes Red Skull who terrorized during it and keeps coming back from it with clones and stuff, and Nazism still gets headlines.
And Magneto's mutant cause is his own precious. The Uncanny Avengers comic where he killed Red Skull pushed his buttons, noting how he still used his anti-telepathy helmet despite Professor X being already dead in order to show he couldn't leave his past behind him, or how he cared more about being a leader within mutants over years than being a good parent to his daughter, and he himself admitted to her he was damned but had to do what he had to do.
So he should use his powers to keep the Ring as far away from him as possible.