I worked on a python codebase for several years that had over two million LoC. The code was well-organized and under constant development by at least ten devs. There were Java components in the larger project that were occasionally touched on, and it was always slower to work with those parts.

A well organized python codebase really is faster to work on than other languages. If your dev work is slowing down as the codebase grows, that's a sign you're accruing tech debt by not keeping up with organizing it.