It’s important to factor in how much cost savings Facebook could realize by eliminating most of its advertising department and associated engineering when looking at how moving off an advertising model might affect profitability. I have no idea what the magnitude of this is, but a good portion of that $30-40 has to get chewed up by spending on stuff that makes the platform less useful to the end users.
FB is on the high end of ARPU. Most other services are cents to low dollars.
https://www.cnbc.com/2019/11/01/facebook-towers-over-rivals-...