I gave up visiting Facebook a long time ago, so can't speak to whatever current algorithm, but even a few years ago, my feed was already flooded with outside content while only presenting a small fraction of my friends' content.

If I wanted to see most of the friend-content I had "subscribed" to, I had to do a manual tour of their profiles.

I'm sure people do post even less now, but I'm skeptical that's the root cause of what's being reported. The explicit bias towards political/commercial/promoted/engagementbait content over "subscribed" content has been there for years.