[assbuttbuttass]

> The fact that a function can perform asynchronous operations matters to me and I want it reflected in the type system.

async doesn't tell you whether the function performs asynchronous operations, despite the name. async is an implementation detail about how the function must be invoked.

As TFA correctly points out, there's nothing stopping you from calling a blocking function inside a future, and blocking the whole runtime thread.

[omnicognate]

I didn't say it tells me whether the function does perform such operations, I said it tells me it can. More importantly it tells me which functions (most) can't.