It doesn't seem like there's much appetite for this to change among social-network founders either: https://twitter.com/nikitabier/status/1403498766737444865
"@nikitabier If you’re building a social app and less than 70% of your users are granting access to contacts, your app is dead on arrival until that’s fixed. Network effects will never form if you expect users—who have a 5 second attention span—to find their friends by typing in usernames."
What options exist for being on populated/powerful networks truly pseudonymously?
It seems like you might have already found your answer: establish a full-fledged bifurcated online identity. Instead of throwaway, create a bona fide secondary/tertiary/etc. number, email, and so on.
The challenge is that the networks are using these identifiers as both connection points and implicit proof of identity/existence. Throwaway/anonymous doesn't work well for the latter use case.