None of the problems listed is inherent in HTML + touch of JS. Especially since most browsers these days will remember what you typed anyway unless specifically instructed otherwise. Complaining about the back button behavior in SPA world seems...misplaced? If anything, its behavior is even worse.
I think this is referring to the server round-trip -- form submit, server-side validation, "you have to specify a color for your widget" and everything on the field is blanked out because the server didn't fill in the default values into the form based on your previous submission.
Back button stuff; I mean, it's not trivial to support it correctly now, and it might just be an increased focus on usability and testing of this sort of thing, but hitting back was always dicey -- half the time you'd get some error about re-posting form data when you hit back, and if you said no, bad things happened, and if you said yes, worse things happened.
Back button works every time if you create pages, and navigate between them using links.
There are some garbage web forms out there, but if we're comparing building SPA in 2020 or webforms in 2020, webforms is unlikely to screw up your back button.
