No one’s comparing Petersen to Lovecraft, that would be ridiculous; and I’ve never heard of anyone giving more ‘respect’ to the former than the latter. No one but the most uninformed thinks Petersen invented any of the Mythos. I would be confident saying, however, that if it wasn’t for Call of Cthulhu, Lovecraft would be known by the general public about as well as Algernon Blackwood or Sheridan Le Fanu are – ie, by afficionados of weird fiction only.
That’s certainly having an impact on popular culture, but of course it certainly doesn’t detract from Lovecraft’s achievements in any way or set up any basis of comparison.
If people think Petersen copies/benefits from from Lovecraft’s ideas – well, people have been copying his ideas since he started writing his stories, and in fact he actively encouraged it when he was alive. He copied other people’s ideas too, like those of Robert W. Chambers for instance.
If he was alive Lovecraft might not have liked the idea of fluffy Cthulhu slippers – then again he might have, he had a decent sense of humour – but he least he probably would have enjoyed the royalty cheques and eaten properly! 🙂