BEM is a decent convention for old-school, global document styling, in the absence of scope. But it's also manual, error-prone, and verbose, making it a poor substitute for actual namespacing provided by components. I sympathize with your resistance to css-in-js; I've been doing webdev since 1998 and only really embraced it in the last couple years. I'm reminded of quotes like "The difficulty lies not so much in new ideas, but in escaping the old."