and it looks like there are other overrides in pages_com_content and blocks_toolbar

A simple source check on any page that has tabs indicates that the css is used. I guess people are confused as they expecting that the scss file should be imported in the template.scss. But this was the way we were building sites a decade ago, these days we try to componentize as much of our code as we could so that the code could be reusable and extendible...

I don't think there's something to do be done here, other than teaching people how to go away from the monolithic css file and embrace the modular paradigm. This will eventually lead to the deprecation of monolithic frameworks like Bootstrap...