Even without watching videos I can confidently say wax potting doesn’t impact 60 cycle hum.
For a start, the railhammers are covered while the Duncan’s are not. That cover is soldered to the baseplate and grounded as a shield.
After that it’s difficult to say what else could be contributing to the noise because there are too many unknowns- what wiring is in there, what signal path you have, and if proximity to any computers or dimmers on the same circuit are having an impact.
Even a Humbucker isn’t 100% silent. The Railhammers in the videos are definitely quieter than the Duncans, but the Duncan’s aren’t unusable by any means.