The question isn't whether or not there's a dispute. The question is whether or not there's a meaningful dispute, and whoever's showing the map still has to make that determination. For example, I still hear people calling it "the war of northern aggression" and calling for the South to rise again. Do we mark everything south of the Mason-Dixon line as being disputed by successionists? No, obviously - that claim is ridiculous. But that claim exists, and so you must decide whether or not it is "legitimate". It is exactly the same process as deciding how to show Crimea or Ukraine or dozens of other international borders of varying dubiousness.
I can see how your point applies in the case of "the war of northern aggression," but not here. If you're showing different things to different people on different sides of the dispute, obviously you've decided there is a meaningful dispute.
"Legitimacy" is a subjective moral argument in and of itself, and is subjective, and likely to wind up on the wrong side of history. Hiter's annexaction of sudetenland was generally discussed through the lens of legitimacy in pretty mainstream conversations. Obviously history looks at his actions through another lens.
If Russia stops at Crimea, it might be an interesting footnote or a hard pub quiz question 30 years from now. If Putin sets his sights next on Estonia, Latvia, or Lithuania, and the West lets him have it, it's going to be remembered much differently. By the way I'm not ominously promising future-Hitler. I don't think Putin wants the west, or any more than that, and I don't think any genocide is in the future.
But I do fear that he wants to rebuild as much of the former soviet block as possible, and I do think the EU won't stop him, which will itself be the final nail in the coffin of its legitimacy, and eventual dissolution.
