It certainly could be a supporting argument. Whether I am confident that Flutter will be used to provide good UX in most cases is a different issue. Haha Yes, I wouldn't necessarily see the Flutter approach as bad if it improves the web. It's just that I think we have enough tools built-in to accomplish good webpages, even "web apps", and many of the kinds of developers resorting to Flutter may be the types who couldn't figure out why their custom-built blog using React is so slow and buggy (it's gotta be the stupid DOM!).

EDIT: I don't mean to crap on React. It's just a common frontend framework.