Maybe it's jealousy, given that Paul was the most successful solo artist out of the 4 of them. They were brilliant as a band, and while Paul did write some 'soppy' stuff, most of the stuff he did was well and truly above what a lot of the other musicians did, then and now. Take Band on the Run for eg; the whole album is one of the best recorded. Wild-Life was brilliant and Venus and Mars had some really good stuff to. But when you consider that all four outsold anyone else, either together or solo, it proves how good they really were. And that includes Elvis.