Most people do not place expansion joints on conduit as needed or correctly. Fitting can loosen. Conduit oxides. Conduit moves.
On the other hand a copper spliced EGC is no different than a phase or neutral splice. We know it holds up.
Many issues with this. It would apply equally to copper or aluminum if true. First as a matter of fastener science google a “Junkers” machine used for testing the self loosening theory. It turns out self loosening can happen but only under extreme circumstances that are impossible with pipe fittings.
Second we need to consider electrical contact theory. With electrical contacts pressure in a bolted or threaded fitting first cracks the oxide coating exposing bare metal. A little bit of both sides of the joint mix, forming metal on metal cold welded contacts called alpha spots. Further increases in pressure increase the number of alpha spots and smear and enlarge existing ones.
Oxide is along the edges, far removed from the joint. Alpha spots are the last to be consumed. Plus metal oxides are the basis for Schottky diodes and surge arresters…hardly the stuff of an insulator. Try Meggering rusty steel. It is almost as good as bare.
Conduit moves but so does electrical cables and everything else. It has little to do with an argument against conduits of trays as grounds,
