Usenet is, Matrix isn't. Usenet achieves this with a broadcast design - every node on the network receives every message. As a result of this and being flooded with half a petabyte of new messages per day, there are approximately 3 (three) nodes (all other providers are reselling access to one of these).

The text side of Usenet is healthier, with a few gigabytes per day, and not trying to retain every message forever. Would it work if it was also the world's git forge though?