How to correctly apply thermal compound to ICs and heatsinks?
The best thermal transfer is metal-on-metal. Thermal grease is meant only to fill voids, not to act as an intermediary.

It should be applied thinly and evenly, then scraped off so that it only remains in the gaps. A properly trained line operator should have no issue with this.

I once had a production issue in an application where a heatsink assembly was being used as a low-voltage, secondary side DC path to an ORing diode. The operators were putting so much thermal grease on the assembly that instead of current passing from plate to plate directly, the only low-resistance path was through the 5 screws holding the plates together. Have you ever seen burnt screws before? Didn't think so...