In Go, once you've FFI'd, you're likely to be able to use the Go data directly in C. In Python, you generally have to crawl over the Python-based data at Python speeds, converting it into data that your C library can understand, and then when C is done, convert it back into a Python data type at, again, effectively Python speeds. Unless you're willing for it to just be opaque data that Python effectively can route, but not manipulate. (This works, but is distinctly less useful. Of course sometimes, like for image data, it's the best option.) Combined with the sibling comment that actually times calls and finds Go is faster anyhow, even if it is a microbenchmark, I don't think your argument carries water.
It sounds to me like you've latched on to some propaganda that you like and are happy to share but don't have any personal experience with. Go's FFI is relatively slow for a compiled language, but it isn't even remotely uniquely slow. Many languages have a C FFI with some sort of relatively expensive C conversion operation, and as I point out here, that actually includes Python in many, if not most, uses (it's pretty rare to want to write code to bind to C that just ships over two integers and returns another integer or something, usually we're doing something interesting). It is the languages like Rust or Zig that can do it for effectively free that are the exception, not the rule. Go's FFI costs are not all that expensive compared to programming languages in general, and if you're worried about the FFI performance, Go also generally needs FFI less in the first place than Python because it's a fast language (not the fastest by any means, but fast), and the higher proportion of Go code will generally smoke Python anyhow. Unless you foolishly write a very tight loop of C FFI code in Go, which is a bad idea in most langauges anyhow (again excepting the exceptions like Rust and Zig), Go's going to outpace a Python program that is mostly Python but uses a bit of FFI here and there by a lot anyhow.
The idea that Go is brought to its knees by a single C call that takes 100ms or something reminds me of the people who think that as soon as you use a garbage collected language you've signed up for a guaranteed 250ms stop-the-world pause every three seconds or something. Is it free? No. Is it expensive? In relative terms maybe. In absolute terms, not really. Most programs, most of the time you won't notice, and if you are in a situation where Python is even a performance option virtually by definition you're in a situation where it won't be a problem for Go.
This is not rah-rah for Go or slagging on Python. This is just stuff engineers need to know. Python is a very capable language, but you definitely pay for it. It is not free. Every greenfield project, you need to sit down and calculate the costs and pick a good tool, but you're going to make dumb, project-killing decisions if you're using costs that are multiple orders of magnitude off of reality. I've seen it kill projects, it's not just theory.