In the movie, that takes place after the Digimon Emperor is beaten, Gatomon and Patamon digivolve to their Mega levels because the others can't beat the corrupted Cherubimon. Which by itself is impossible for them. They digivolve to release the golden digieggs to allow Veemon and Terriermon to trasform into their golden forms. But the series pointed out that the golden forms aren't strong enough to match Ultimate digimon. One level inferior to Cherubimon. Not only that, but fucking Patamon and Gatomon digivolve to their Mega forms. Their Ultimate forms alone beat the shit out of most bad guys, but they get taken down in one hit here.
Then at the end of the series, the characters are trapped in a parallel world that makes dreams and nightmares come true. They all split into all their trasformations and MagnaAngemon is present. MagnaAngemon is supposed to be strong enough to kill a Dark Master with ease. But not Malomyotismon. Even though he was powered by dreams. Not to mention the forms from the movie aren't present. And the movie is in fact canon.