Entirely valid critique, and not one I really have a great answer to. The best we can do for now is to attempt to decentralize things as much as possible at a design/architecture level.
Nostr takes something good from Email in this sense- it is monopolized, but the fundamental openness of the protocol allows for competition to exist (Protonmail, Countermail, etc).
Ultimately I think we need to "re-negotiate" the "social contracts" that make up the way we use the internet. I don't know what that will look like, but I do know that we have decades of mistakes to look back on. I am an optimist at the end of the day, assuming the global order doesn't collapse too soon and cause us to regress early technologically (which I would not really be opposed to, honestly).