^That makes sense. For example Charizard X would have increased attack and decreased sp. atk. and vice versa.
Yeah, I'm betting we'd see quite a few reductions in a few other stats for those with more than one boosted stat, like Mega Mawile and Mega Absol, who have Defense/Sp. Defense and Attack/Speed boosted respectively.
But yeah, given at least one stat will be boosted, there's a good shot another will be greatly hindered to make up for it.