The most surprising thing is that there's people who think LinkedIn used to be good. It was built by spamming people and grabbing contact books without consent. It's always been trash.
It was trash, but dealing with recruiters has always been, and keeping professional network into a separate space was the saner thing to do. In that sense, I think it worked as intended: people would only need to react to recruiting mail, and that only during the spans they cared about moving careers. The whole "tell your life on linkedin !" promotion pushed by Microsoft clearly degraded that part.
My last role was gained by reaching out to a colleague I haven't talked to since college and asking about the role I applied to, and he was nice enough to give me a referral (I honestly wasn't expecting a referral. it was easily 5+ years since we last interacted, didn't talk that much in college, and I wasn't the best student to begin with). I doubt he posted his roles on Facebook so I never would have thought to contact him otherwise.