CSS by default is not messy to manage. *Teams* using CSS are often messy to manage, but that comes down to poor communication and poor habits. Fixing that with technology that encourages bloat and bad habits is a dumb idea.

I'm SO impressed by your 12 years of experience. I built my first website with HTML + CSS in 1997. In 2008, I worked for a company that was basically a sweatshop where several times a week I was asked to build a new website that had content that had comment similar to like the last 20 sites I'd built, but looked completely different. I had about 6 hours to reskin it and change out the content--and it had to work in IE6 and Netscape Navigator. There's a reason we stopped using the font attribute and similar, and that's because it really is a lot more maintainable to separate presentation and content. It's also amazing to be able to specify a style for your buttons, for example, and have that flow all through your site without your having to add code to every button to make it work.

The main reason people have to use !important is because we use all these libraries we don't have control over that use things like CSS modules that mean you can't just override the style from outside at will, yet we also have designers who don't give a flying what the library actually supports. A lot of the problems you think are due to the "messiness" of CSS are due to all these tools that have burrowed into the modern dev experience that prevent CSS from working as intended, by a bunch of people who have never done it right or even seen it done right. Because they are learning everything third hand from people who also have no idea how this stuff works.