While I don't have any hard numbers, I would bet a lot of money that any "slowness" of ansible has nothing to do with the use of Python. Everything happens over SSH, that's a lot of network roundtrips.
SSH can be quicker, I believe ansibles use of SSH processes is more the issue. An old but still relevant benchmark exists in my pyinfra project which uses SSH (amongst other protocols) but a Python implementation, and its significantly quicker and more scalable than ansible: http://docs.pyinfra.com/en/1.x/performance.html
Indeed. See saltstack for something that does the same thing, witten in python that runs much faster.