This is something that I see espoused by "web traditionalists" for lack of a better term. Sure, there are a lot of web developers who are not optimising for performance but I think the difference is that it has simply shifted to the frontend where it's more noticeable. The kinds of people who care about performance in the backend are exactly like the kinds of people who care about performance in the frontend. There's…
SPAs being the darks ages is over-the-top, but being an SPA when other web architectures could better serve the user is a dark pattern . That tax app doesn't need to be an SPA. JavaScript powered interactions make the experience nicer for the user, but that doesn't mean it needs or is improved by being a single page.
Email is a great example of this - GMail, at launch, had much better UX than existing server-rendered applications like Hotmail.
You can find bad UX everywhere - in SPAs and server-rendered interfaces alike - but there’s nothing implicit to SPAs that reduces usability.