Modern CSS has _some_ of the features of SCSS/SASS. It does not have all of them. But most importantly, many of dependencies one might want to use also make use of SCSS/SASS downstream. If you're happy to build everything from scratch and eschew any dependencies that require a build system, then have fun explaining to your product person why it took so much time to build a thing that they know very well is a pre-built component in some frontend library somewhere.
> Modern CSS has _some_ of the features of SCSS/SASS. It does not have all of them
You say it like more those features are desirable.
> then have fun explaining to your product person why it took so much time to build a thing that they know very well is a pre-built component
Sure. I wasted more time getting an assortment of pre-built components to behave than I did building the basics from scratch. And then comes a breaking change. And then that component library uses styled components and doesn't run properly on the server. Why do people do this to themselves?
Modern CSS is amazing. Why on earth would anyone use SCSS? It pays to look at what Vanilla can do these days.
> Even a "thin" layer of JS on top requires some degree of dependency management
Use modules and import away. If it is truly a thing layer, there's no need for further optimisation until far along in the product.