And yet 90+% of those SPA-apps have worse performance.

This. I fully get the in-theory argument that a thick SPA can make for a smoother experience, but that just makes it all the worse that all but the most exceptional SPAs are significantly worse in terms of responsiveness than a series of server-side rendered pages. (even gmail, which is pretty good they go, is laggy and can easy eat up 1GB of RAM)

The fact that people will copy/pasta from stack exchange, or add in massive packages from npm that do things other packages in other areas already do doesn't mean it has to be that way.

A dresser can be hand crafted from solid oak and built to last centuries, or it can be flat-pack barely better than cardboard with fake plastic oak veneer.

You can make a fully functional SPA with less than 1mb of payload, or you can create the hot garbage that is Jack In The Box's menu website, that delivers 48mb of insanely bloated JS garbage. And I only harp on them because it's the single worst SPA example I've seen to date.

For that matter, I think with some nice tooling HTMX can be a pretty great experience for most in-between usage.