> You cannot spin up 100K native > threads to handle 100K requests that are IO bound (which is very common in a microservice architecture, since requests will very quickly block on requests to other services)

The Varnish server does that all the time and it is not a problem.

Modern OS handle a large number of threads much better than 10 years ago.

In case of python however, you can not do that due to the GIL and the fact python handle native threading terribly.