> Async in Rust and C++ is nothing like it is in Python or NodeJS. Choose your own runtime is a very different model than having a default one.

Python still has pluggable eventloops - this is sort of mandatory to interact with weird things like GUI toolkits, and Python's standard event loop was standardised pretty late in the game. Early on there was even an ecosystem split between Twisted and competing event loops implementations.

> For example both Python and NodeJS use a single thread to execute async code

I'd argue this is more a historical artefact of how the languages functioned before futures were introduced, rather than an inherent limitation.