The Magneto - have origin stories that Marvel will never change. These are some of Marvel's oldest characters, and in Captain America's case, the character even predated the company (at least the company known as Marvel; Timely Comics was a substantially different organization). The origin stories of the two will never change - but is that a good thing?
Marvel's "Sliding Timescale" is a unique narrative device in which the origins for multiple superheroes are not given an exact date, and thus can be moved around at the company's whim. This ensures that characters won't run the risk of appearing extremely dated if, say, their origin takes place in 1963 (like Peter Parker, but an actual year is not mentioned, and Marvel in fact rarely mentions years just for this exact reason). While Iron Man's origin clearly takes place during the Vietnam War, the country's name is rarely mentioned in subsequent issues, and was actually changed to Sin-Cong in the official timeline.
But Stark's cinematic origin was shifted to Afghanistan in 2008's Iron Man, and his wasn't the only origin updated for a more modern audience. Peter Parker was bit by a genetically-engineered spider instead of the famous radioactive arachnid in Amazing Fantasy #15. But Captain America and Magneto's origins are rooted in World War II; America was just emerging from the Great Depression and a symbol of American ingenuity was needed, especially with a conflict with Hitler on the horizon. Captain America could be created in, say, the 1990s, but a modern origin wouldn't have nearly the same impact.
Meanwhile, Magneto's origin is rooted in the Holocaust. Writer Chris Claremont fleshed out Max Eisenhart's backstory with one crucial detail: that Magneto was a survivor of the single worst atrocity committed by humankind. Again, it's hypothetically possible that Marvel could move his origin to the Apartheid era in South Africa or a modern-day Chinese concentration camp for Uyghur Muslims, but the Nazis codified systemic hatred in such a way that it could never be sured. This means Magneto's age is fixed and the character only gets older with every year, but it's heavily hinted that his powers slow the effect of aging anyway (and in a comic book universe where clones and time manipulation exists, this is hardly an insurmountable problem).
There is not a single aspect of history that the Second World War did not effect, and comics are no exception. Perhaps Marvel's inability to change either character's origin is a positive outcome. The best and worst of humanity was on display during the conflict; Captain America represented the best, and Magneto survived the worst.
