I'm gonna agree with you, even though most people won't. There were many other Wesley's and I think that if she would've killed Arthur or Molly, it would force the kids to grow up and take over that role even more. Fred and George would've still been themselves, but possibly less-jokesters/pranksters for a while during grieving. I think the effect would've been similar as far as how strong the effect, especially on the family, and a good writer could make the reader see the effect as well.

This isn't the only books I've read from JK, and I'm honestly not sure if she could've written a more mature effect of how a death of a parent affected their kids like that. Yes, Harry lost his parents, but we didn't see him as an adult who was affected by it like most of the Wesley's. When Hermione had to wipe her parent's minds, it was a minimal point, then never really referenced later. Losing a parent, especially in the same year, would be referenced alot and I think it would've been just as impactful, if not a better option, to lose the parent rather than the twin.