And based on the word of the creator, Sky form Shaymin, Black Kyurem, White Kyurem, and Resolute Keldeo are all "new Pokemon" and not Pokemon forms. While were on it Keldeo's Resolute Form is "Supposed to be stronger than his original form" there was no stat change with it. They hyped it up as his stronger form for both the movies and when he was released for B2W2. They can still be stronger even with a debuff, change in type for Ampharos and different abilities like Mawile's Huge Power makes them stronger already. Having different stats makes them stronger as well, but they'd still get debuffed to balance out the changes.