I clearly asked which rule changing height/weight violated. Nowhere has it been established that this is impossible in the GoT universe, and we have seen far more outlandish things when compared with our own universe.
It's about suspension of disbelief. Like how no one has an issue with Superman having super strength, speed, vision, etc., but it's ridiculous that no one recognizes him in his "disguise" of a suit and glasses. The rules of the Superman universe clearly establish that the character has all those powers, but otherwise the world is very consistent with ours, so no one recognizing that it's Superman with glasses on is laughable. While GoT is not high fantasy like LOTR, there are still a lot of fantasy elements in the show and we have seen magic produce all sorts of things that aren't possible in a world more grounded in reality. To suddenly be upset about the physics of a character transforming is blatant nitpicking.
This isn't to say I like the Arya story line either, because I haven't since she arrived in Braavos in season 5. There is plenty of legitimate criticism in her story without trying to go after things that are plausible because of magic.