> I'm not 100% clear on .pyc files TBH; I'm guessing they speed up start time?

They do.

> Are we losing out on performance of the actual installed thing, then?

When you consciously precompile Python source files, you can parallelize that process. When you `import` from a `.py` file, you only get that benefit if you somehow coincidentally were already set up for `multiprocessing` and happened to have your workers trying to `import` different files at the same time.