I've been thinking similar thoughts recently, in that I am not sure that a function call is the best way to model asynchronicity. Io-uring in particular feels much more suited to a req/res type model, which has the benefit that you can make a single threaded state machine the core of your app - very pleasant to test and reason about.

I'd draw the analogy to RPC; it's a leaky abstraction because HTTP is fundamentally a different thing than a function call. I'd argue that event loops are a different thing as well.