I'm ok with changing the default threads number limit.
Not sure about numbers.
If you want to limit to 16-20 that may be ok but `cpu_count + 4` doesn't work in this case. On cloud servers, I see 128 or even more cores very often. 160+4 is not that you want to propose, sure.

I insist on changing the default calculation schema in concurrent.futures, not in asyncio. There is no case for asyncio to be exceptional.