Hello Phaerie

(does that mean fairy?)
umm.. sorry phaerie (lol that rhymes) but i disagree with you there. he got beaten by james and sirius as they were as good as him , outnumbering him and he was taken by surprise. being a deatheater and a member of the order, i would assume he is good at DADA.
as for DD refusing him because he failed, that is a supern solution in its simplicity, it would completely knock off all the theorising that we have done. however that would be a tame wont it?