I grant that Facebook is showing us what we want to see, but I don't believe that their one-dimensional model is truly reflective of what we get to see.
I have a lot of left-leaning friends. I get a lot of Sanders vs. Clinton ranting, mostly from crazy people my friends are apparently connected to somehow. I consider them noisy and annoying. But their existence makes it clear to me that there are multiple left-leaning feeds.
Similarly, there are multiple feeds on the right. Looking at the WSJ red feed I see nothing from us #NeverTrump people, which to me points to the problem with a one-dimensional analysis of Facebook's algorithms. (Or, donning tinfoil, it may mean that the WSJ is in the tank for Trump.)
Facebook has not yet presented me with pro-Trump articles, though I get my share of anti-Trump articles from a conservative viewpoint in my feed. This is after all what Facebook thinks I like, and they're right.
All this is to say that my own experience tells me that in fact Facebook's feed algorithms are much more nuanced than a one-dimensional analysis can show.
I have friends who have said they like being able to see a red-shifted feed. I endorse that. But it's not really something I miss from Facebook, because I already have RedState, the National Review, and The American Conservative in my normal political reading.