I agree - fake!Moody has always been too helpful of Harry's DADA skills, IMO. He goes far beyond teaching Harry just enough to get through the tournament, and teaches him some seriously useful stuff for fighting Voldie... Another illogical/inconstistent moment, I think.

Good question... I would hazard a guess that Harry sucks at occlumency because no one has told him how to do it properly. Whereas to resist imperious, he just has to be his usual stubborn self. ;)