You aren't wrong, but at least in Spider-Woman's case, Queen Veranke posed as Spider-Woman for years on our time, probably not so much in Marvel time, but that story lasted and she did a lot of damage, even if the image of "Skrull Spider-Woman" was used very briefly and mostly in marketing materials. There was still a more lasting impact in the stories beyond the original reveal of Spider-Woman being replaced by the Skrull Queen. That story ended The Initiative, spawned Secret Invasion, her death by Norman Osborn turned into Dark Reign, which lead to the Heroic Age, etc. It's also a reminder that the entirety of New Avengers up until after Secret Invasion, the Spider-Woman on that team was an impostor.
Vision appeared like this for about 2-4 pages, was promptly replaced by Jonas (Vision 2.0) and was eventually rebuilt. Doesn't hold the same historical weight as Skrull Spider-Woman.
Then there's the fact that aside from what happened in the comics, the Skrull head just looks better than Melt Head.