[Pauan]

Threads cannot scale at all, because you're limited to the number of threads (which is usually quite small).

Async code can scale essentially infinitely, because it can multiplex thousands of Futures onto a single thread. And you can have millions of Futures multiplexed onto a dozen threads.

This makes async ideal for situations where your program needs to handle a lot of simultaneous I/O operations... such as a web server:

http://aturon.github.io/blog/2016/08/11/futures/

Async wasn't invented for the fun of it, it was invented to solve practical real world problems.

[vacuity]

Threads, at least on Linux, are much more lightweight than you seem to think. Async Rust can scale better, of course, but you're overexaggerating your case.