Defiant/Competitive and Weakness policy is the heart of bulky statbooster builds. They are pretty powerful, but by no means broken enough to get banned. Weakness policy is not overcentralizing by any means because a lot of pokemon prefer band/specs for the immediate augmented damage. And of course, there is a hard counter to statboosts called unaware. I believe that Magic Bounce is not actually that broken because defiant/competitive teams can punish it hard by bouncing off debuffs to themselves and gaining power boosts. Imposter Blissey is good but it matches up poorly against things like simple weakness policy.
I am expecting Aerilate and Pixilate to become more viable because Steel types no longer wall them off, and it would benefit against ghost types, which would probably appear more often since it is a great type in metronome. Aerilate matches up well against Mega Venusaur which is a solid bulky statbooster and Pixilate matches up well against Mega Sableye. Refrigerate is good but Ice is a terrible defensive typing. Not a big fan of Galvanize because Ground types will just negate it completely. These are some teams that I theorycrafted.
Aerilate:
https://pokepast.es/788b1af71145b1d8Delta Stream on Dragonite because both mons benefit greatly from it and it mitigates their crippling 4x weaknesses.
Pixilate:
https://pokepast.es/8f41102e191c482fChoice Band is the item for the Mega Altarias because most normal type attacks are Physical and it would be hard to proc weakness policy because of their great typing.
Pixilate+Fairy Aura:
https://pokepast.es/c5ae96c0ceb84364Probably not optimal but I just wanna see how much damage a banded pixilate + fairy aura boosted mega kick can do