I run a movie blog and have seen MASSIVE dropoffs in referrals/engagement on FB - As it's just me running the site, and my time is zero sum, I have shifted far more of my focus on email newsletter marketing as it drives far better traffic. I tried paying to promote a few posts but the ROI was definitely not there relative to ad revenue.
I have heard from countless other publishers I know who are doing many similar things as to not get trapped in the FB ecosystem.
This can be compounded by the fact that a lot of pages that have a % of fans that are from "Like farms" have no easy way to filter those out. So now those companies are paying to reach a garbage-quality audience with an incredibly poor signal to noise ratio.
I have heard from countless other publishers I know who are doing many similar things as to not get trapped in the FB ecosystem.