The argument was that Facebook is neutral as a platform. Similar to the internet, it serves all kinds of content. Some of the content is good, and some is bad. That doesn't necessarily mean the platform is good or bad.
Having worked in growth before (not at Facebook), I can tell that you vastly underestimate the impact FB teams have on how/when/what/for how long/how many times/etc content is displayed to end users. This is absolutely not a neutral impact.