I do not post much here but do have a back ground in body shop as well and agree with you.
But epoxy and 1K both stick or bond to properly prepared metal.
It is though as you stated that the epoxy seals the metal and the 2K is porous.
Being that 2K is porous I would do just as you stated.
Use epoxy, to seal the metal then top coat with 2K whole within the window of what is recomended on the tech sheet. PPG has a day window the primer or paint top coat will make a chemical bond within this period. If not it must be scuffed as what ever top coat going over it will now be a mechanical bond.
Most epoxy can not be sanded so scuffing it is. That is what PPG says to do with their epoxy products.
I agree no way would I skip epoxy on anything that is a long term project like he has. This step should not be skipped.
I also mix one part PPG epoxy with paint grade laqure thinner as a sealer before paint as recomended.
It is good insurance.
