USENET very much depended on ISPs in practice, they ran most of the servers!

However, yes it was theoretically possible to have a route between two NNTP servers that wasn't over a BGP-routed chunk of internet but was "something else". Including posting a tape.

In the original architecture yes it was closer to an ideal. If only Usenet became Xanadu. Unfortunately people gave way to the centralization of servers and thus lost control to the direction of the 'net. At least that's one take.