I’m not sure it’s a waste. Yes, CSS layout is complex, bordering on stupidly complex. But I’m not aware of any other reflowable layout system of comparable power. The sheer amount of pain it takes to wrangle something like CSS floats out of TeX—on a fixed-size page!—certainly makes me appreciate just how difficult the problems CSS solves are.
Though it sure would be nice if people were exploring other approaches to reflowable layout without tying themselves to CSS and modern browsers’ codebases.
When you want to do something simple but you have to bring the entire philosophy of CSS into consideration to figure out what the right way to do it is.
Its a common misconception that CSS is easy, that's its not a programming language. Its however one of the most difficult to understand. You can write CSS a whole career without understanding the basics, and responsive design made it exponential harder. And there are popular anti-patterns such as trying to overwrite an existing css file... But if you do learn it - its very powerful, and much better then defining design rules in JS or XML or a graphical design tool.
Doing it in browser. Android, iOS, native macOS apps, QT, none of them have the insanity of layout that is CSS. I bet most other frameworks don't as well, but those are the 4 I'm familiar with. CSS is the odd man out when it comes to being utter shit at layout, and yes that is including flexbox and grid.
That you have to redo it all the time, as in kitchen remodels.
Blame it on folks outside of dev? I would ban the word “modern” if possible. Everyone thinks that it’s obvious but no one seems to be able to define it once and for all, lol