As another example, I know of a rider who won quite a bit as a junior. When she went to college, she put on the "freshman 15" and then some. She showed in the IHSA at school, and she still won a lot, since she was still a good rider, and rode rings around many of the other kids who did not fare as well with the IHSA format of hopping on a strange horse and jumping around a course with no practice.
So regardless of the perception, the fact is that riding ability is more important than size or shape. If more people can grasp that fact, all the better.
As for GM, I have the utmost respect for his abilities and accomplishments with horses. That doesn't mean he's perfect. Or that every word he says on every subject should be taken as gospel.
And anyone who thinks this is a new problem is showing their lack of mileage. The new twist is that maybe it's more widely known and discussed. (A Twitter feed? Really?) The problem itself is not new.