The two schools of thought are probably both correct depending on the size of the job.

Seems to me that you would be OK to do the body work and then seal the work with epoxy primer when doing just "a spot repair". But when doing a large area like a blasted body or frame, I think you would be better off sealing the whole area first then doing the body work on top of the epoxy sealer. Reseal the repaired area.

My question is what experience has anyone had with doing body work and final paint "on top" of powdercoat primer?