I've run into the import issue as well, it's especially painful if something imported is doing work using a slow library (e.g. a config module loading a HOCON config using pyhocon a.k.a slowasmolasseshocon)
The problem you mention can be significant because some design patterns in Python encourages this. Eg function arg with a default that’s expensive. Unfortunately this whole speeds up repeatedly calling the func, the cost is paid at first import.