I guess I see this differently as I see him presenting his work more as an 'idea' with the actual final images not meaning very much more than them being striking images.
He copied comic book panels - that was his art, his final pieces (the Russ Heath one inc) are just the way of presenting his 'art'. It really didn't matter whatsoever what panels he copied, what mattered is that he did it, no one else, that's his talent.
Now I can see people then countering that with 'anyone could do that!' - but yeah, well they could, but here's the kicker... they didn't did they...
Just as placing a moustache on the Mona Lisa and exhibiting a urinal is artistic, so is doing what he did.
Undoubtably Russ swiped art when drawing his panels, every artist does. The difference being, that was his artistic sphere, his work sold in the millions for 10 cents each time. Roy's sold one each time for millions.
I'm not even a Lichtenstein fan, but talent is talent.
But hey that's my opinion, your mileage may vary.