There is no doubt that McCartney was a brilliant songwriter and hugely influential. The two songs you mention have similarities but that's about it. It's probable that neither will be listed among his greatest works although I've always felt the criticism of them is unfair. They were MEANT to be simplistic. In the case of Mull of Kintyre, he wanted to use bagpipes but was limited by the restricted range of that instrument. Anyway, I'm sure Sir Paul doesn't need me to defend him. I hear he's made a few bob from his songwriting.