It really depends on what you're doing. In my experience it's quite common for moderately complex python web services to be mostly CPU bound if you put the database server on the same machine.

If you're talking to a regular sql database you'll usually find the database itself limits concurrency so there's little advantage to async io over threading. You really only see the advantage of async io in proxy like scenarios or where you're managing thousands of long lived connections (web sockets etc.)