pretty sure Phoenix with Elixir can handle that load too.

Elixir/Erlang is really slow. The strengths of Erlang/Elixir is easy multithreading, easy distributed computing (just as easy as local multithreading), easy fault tolerance and easy low latency. If you have to do something single threaded and performance critical then you do the same thing in Erlang/Elixir as you do in Python: FFI to native code.

I wasn't implying Elixir/Erlang was fast.

My statement was that it could handle the load. Taken into account the fact that the language is built around concurrency, it would handle the load within multiple threads without a hitch.

HTTP is not the bottleneck of anyone's application. Any interesting business logic will almost certainly cause Python to perform worse than Java, Go, etc. I'm also skeptical of the maintainability claim, because I write Python professionally.

Writing web code in c isn't my idea of easy to maintain

If you used this framework you wouldn't be maintaining web code in C.

That's why you write in Python and use this library

The Python part would slow the whole thing down again.

Anything not written in assembly would slow things down. But very few developers write web apps in assembly these days.