Aren't we making a few assumptions there?
The salute inconsistency was more widespread than you think, though the effeminate arm flap was Hitler trying to do an army salute. If you look at Goebbels doing it he looks like half an albatross. The Army version was normally best done by the SS, the rest of the army had a standard salute, many of the officers refusing to use the Nazi one, hence the occasional ear tickle by AH, to keep them sweet. The SS regiments were the other way round, largely.
I think the point is that as a poltical salute it was not defined very rigidly at first, and so the people who had done it longest did it worst, so to speak.
I think it was originally designed by Ernst Rohm any way. Like much else. His thanks was to be assassinated for being a leather pervert drag queen. And not hushing it up like Goering.