I would call it: "They are essentially using the plain async conversions of regular system calls and Stream (e.g. known from Java/.Net) APIs" All the reactive

I would call it: "They are essentially using the plain async conversions of regular system calls and Stream (e.g. known from Java/.Net) APIs" All the reactive streams stuff still had been push streams, just with some backpressure bolted on. The issue was that without async/await, you always end up with some kind of callback model, which then again results in a push model. Whereas with async/await you can just mostly model IO like any kind of synchronous IO.