I agree it's really narrow in practice. But the basic idea is that Free/libre pertains to your 4 freedoms while open source is about technical craft through a superior design philosophy. There are also historical considerations as OSI was derived from the initial Free software movement and was historically designed to appeal to corporations.

Stallman is very influential for his pioneering of Free software and the GPL/copyleft. But that's what it's limited to now. If you want an example, I contribute to GNU Guix which has put out a statement against Stallmans continued role in representing GNU.

People have very conflicting feelings about Stallman because the campaign for his removal was to be frank, a total clusterfuck. I'm not a Stallman supporter by any means, but it was bad.