MW is not 160. MW is between 154.1 and 160. Assign it whatever label you'd prefer, but the fact remains, he's fought at MW 5 times already.
A true middleweight is 158ish to 160. Canelo was a fake middleweight. That's what Oscar said and he is HOF ATG TBE GOAT. "He's not a true middleweight."
A true middleweight is a fighter that cant make 154 anymore and moves up to 160. End of. Canelo is smaller in height than GGG but thicker set
Miguel Cotto didn't consider himself a "true middleweight" when asked by Kellerman after the Daniel Geale fight, and of course that's who Canelo beat to become the lineal middleweight champion. Cotto was technically fighting at the middleweight limit and was the middleweight lineal champion. How people use "middleweight" in common parlance isn't necessarily the same as what's technically considered a middleweight fight in the rules.