> The beauty of the Web stack is that all of what you are describing is optional.
The problem is not that you cannot write lightweight accessible and beautiful websites, you can. The problem is that this is now all part of the "default web browser" and so many people are taking advantage of its widespread availability to use it without a good reason to. Most commonly fingerprinting, tracking, following corporate dev fads, etc. And because of that it is now borderline impossible to have a decent experience using a lightweight browser because so many websites make crucial use of stuff they should really not. It's possible but it takes time and know-how, personally i don't find it fun enough to invest more time than crafting my ublock whitelists. And this is already more than most people (even people that would be able to do it).
I don't have a strategy for fixing the entire ecosystem, but for my little corner of the world, I guess I've constructed a mental venn diagram where I only browse at the overlap of "content I'm interested in" and "sites which are accessible to me", and leave the rest of it alone. There is more than enough for me to browse in that space, especially combined with my own websites, that I rarely even think about the horrors you mention.
One of the coolest things about it is that I have noticed over time that obnoxious frontend correlates very strongly with crappy content, so the average quality of what I read and watch has improved drastically. I try to practice a "mental diet", and it has helped tremendously with that.
In some ways, it's not unlike IRL, where there are places I would rather not be, and they have certain tells, and I'm OK with them being there, I just don't go inside if I can help it, and I leave as quickly as possible if I do.
I think the Web is still very young, and now that we have can have ML-assisted markup generation, accessibility will be coming around, just like wheelchair ramps became the norm. Pretty soon, we won't be dismissing a 0.01% browser as not worth supporting, because it will be so much easier to just tell the server, "please remove JS and all but the minimal markup from your pages".
If you want to see a PoC of what this may look like, here is a quick demo video. The NoJS bit is at about 2:30. https://vimeo.com/828698165
The problem is not that you cannot write lightweight accessible and beautiful websites, you can. The problem is that this is now all part of the "default web browser" and so many people are taking advantage of its widespread availability to use it without a good reason to. Most commonly fingerprinting, tracking, following corporate dev fads, etc. And because of that it is now borderline impossible to have a decent experience using a lightweight browser because so many websites make crucial use of stuff they should really not. It's possible but it takes time and know-how, personally i don't find it fun enough to invest more time than crafting my ublock whitelists. And this is already more than most people (even people that would be able to do it).