I feel qualified, because I’ve been a SWE for 20 years, have worked in lots of domains (including web, sometime ago) and so I feel I am able to draw comparisons.

Not for nothing, but when I wrote a couple of web apps recently (most recently a market monitoring tool and a physics simulation in wasm and webgl for rendering), I tried different frameworks, but always ended up dropping them. The end result is snappy and fits in kilobytes, and the freaking back button works.

I did of course use some libraries for rendering things like graphviz. I am not a crazy person. But I fail to see what value e.g. react.js* adds, or why there are libraries to wrap websockets.

* For react specifically, I can actually imagine scenarios where it’s useful, but in practice, 95% of places where it’s used should have probably just been HTML with some minor JavaScript for bits of interactivity.

I've also worked as a SWE for many years, and I can tell you hands down that self-rolled frontend codebases are _always_ harder to maintain and add features to, than ones that lean into frameworks and libraries. They are shared understandings that are easily transferrable between contexts.

You don't mention maintainability in your examples, purely things like back button support and disk footprint. They're just pieces in the puzzle.