I don't think Harry was an heir of Gryffindor, but he WAS a true Gryffindor. If anything, I think he was a descendant, just a bit, of Slytherin, and definitely a descendant of the Pervells, making him and Voldy distantly related. Dumbledore, on the other hand, just might have been the real heir of Godric Gryffindor. He seems like the one to be.