This is not what is happening with flask/uwsgi. There is a fixed number of threads and processes with flask. The threads are only parallel for io and the processes are parallel always.
Which is fine until you run out of uwsgi workers because a downstream gets really slow sometime. The point of async python isn't to speed things up, it's so you don't have to try to guess the right number of uwsgi workers you'll need in your worst case scenario and run with those all the time.
Yep and this test being shown is actually saying that about 5 sync workers acting on thousands of requests is faster then python async workers.
Theoretically it makes no sense. A Task manager executing tasks in parallel to IO instead of blocking on IO should be faster... So the problem must be in the implementation.