What does matter is what their primary goal is- Is it to increase user engagement for its own sake (and ad revenue is an incidental necessity), or is it to increase user engagement to maximize their ad revenue?

That is, is the main goal of Facebook to engage and connect people via its platform, or is it to make money from selling ads?

From everything I've seen from them thus far, I just don't believe ad revenue is their main goal. They do seem incredibly obsessive about engagement, but ads seem like a neglected afterthought.

What it feels like to the user is vital. The AI is probably to find the most engaging way to display ads. More engagement with ads == high ad valuation.