CL implementations do have an FFI that you could at least call C libraries from, don't they?

I think so? I honestly don't know, I never really worked with the CL codebase, I just used it for reference sometimes. But even if it did, I'm not sure how much velocity is gained by using CL vs. Python, especially when making a web app, where there are so many examples, libraries, and frameworks out there to help in Python.

While I have admittedly limited experience with it, CFFI worked awesome for the couple things I tried to do with it. I don't have any CL code in production yet, but enjoy using it when I'm doing some recreational programming, or looking for something that's easy to embed in a C program (Lua's nice, but it's trivial to take the ECL Common Lisp implementation and hook up emacs-slime to it, even when it's embedded in a C program)