What you're overlooking is that CSS has to be backwards compatible to as great an extent as possible. It's not an option to abandon existing paradigms and what you perceive as "pointless complexity", because it would break the web. These things inch forward because they have huge ramifications for the internet.
Your rant about back-end/SRE/DevOps being inherently more difficult comes off as ill-informed. Where do you get the idea that balancing performance, cost, maintainability and monitoring are trivial on the front-end?
„my static blog and I cant get the text centered, damn css!“
instead of
„basically a full blown native application but written using browser APIs, with live collaboration features, GPU-using code where performance matters, oh and did i mention it must also work and look good on a mobile screen?“
Re: your second paragraph, I should have said "at scale".
I don't think I'm ill-informed, I've spent at least 5 years in each of front-end, back-end, and SRE/devops...I won't deny that there are some things that are really difficult on front-end (and in fact I don't like doing it because I don't find the challenges it offers very rewarding, though they take a lot of time), but in my experience, back-end is much, much harder at scale.
But the big distinction is that whereas frontend design/architecture/concerns are roughly the same no matter how many users you have, difficulty of back-end scales (about logarithmically) with traffic - 1k DAU is trivial, 100k is easy, 1M is "interesting", 10M is starting to get hard, 100M+ and you need to be top of your damn game (with a team to match) or you fail hard. Most projects don't have to ever reach the difficult regions, but to be perfectly honest my (non-side-project) backend work has all been in the large scale regime, so maybe for the average project across the industry the relative difficulty is about the same.
If you're in "git push heroku main" territory, then sure, frontend is probably a lot harder than backend.
To the first point, that's all fine and good, I think you're actually correct, I'm just tired of the fanboy-ism around CSS, and maybe I'm bitter because of how obnoxious the fanboys we're back when it was truly unusable. 10+ years ago there were people arguing vehemently that things like flexbox were completely pointless and in fact DANGEROUS because CSS was already perfect and could do anything as long as you weren't a noob, which was just ridiculous and wrong. I'll accept that things have gotten a lot better now and the stakes really are much higher w.r.t. changes.
Your rant about back-end/SRE/DevOps being inherently more difficult comes off as ill-informed. Where do you get the idea that balancing performance, cost, maintainability and monitoring are trivial on the front-end?