UE5 source build packaging takes 2 hours vs 2 minutes (launcher)

I’ve built UE 5.7 and 5.8 from source, and I’m seeing a huge difference in packaging times compared to the Epic launcher version.

Using the launcher build, packaging the exact same project takes around 2 minutes.
With the source-built engine, packaging from the editor takes up to 2 hours.

The project and settings are identical, but with the source build the engine compiles thousands of files during packaging (often 1000+ actions), while the launcher version does not appear to compile anything and just runs Copy/Cook/Pak.

Has anyone else experienced this kind of difference between source builds and launcher builds?