I also denounce the notion that trading language complexity for slowness is the case. Python is already complex, and there's some language and frameworks that are actually quite a bit easier to use for web backends. Like java, or dotnet. It just makes no sense to use python for this usecase, even if you ignore the slowness.
But that's not completely true, there is one very good reason to use python. Your devs know it. But, that doesnt say anything about the language itself.