I agree and disagree. Your post reminded me of something else that bothers me, and that's that these girls are throwing these highly public tantrums at their agents. Agents are there to provide the kind of "product" that clients want. Clients seek the kind of girl who's going to sell the product to the most people. And the people determine what kinds of advertising they support by buying products with skinny models, or with Gigi. It's not the fashion industry that determines what's beautiful or we'd all be wearing Iris Van Herpen on the streets, it is ultimately a democratic process. If skinny models didn't sell the clothes better, the industry wouldn't use skinny models.
So if you really want to change the way the modeling industry works, if you really want to point the finger at someone, stop shitting on the messenger and make your pleas to the people actually buying the clothes.
Well, regardless of who is "deciding" what is beautiful or not, I think that the point these girls are trying to make (and badly at that) is that the definition of 'beauty' needs to change and not be so focused on being super skinny. While I obviously love the super skinny look and prefer models that conform to that ideal, I think there are much better ways that these girls could get their point across. Slamming their agents is the wrong way to go about it.
I found an article by an Australian commercial model, Jessica Gomes (on the curvy side, probably an Australian size 8). She's asked about her views on the pressure to be super skinny and she manages to answer the questions by not slamming her agents or criticising other super skinny models (too much). Yes, she notes that being too skinny can be dangerous, but she doesn't "blame" her agents or anyone else. She also doesn't glorify plus size models by talking about how amazing Robyn Lawley is, or that women can be beautiful at any size. Instead emphasises that it's important to be healthy and exercise and she notes that as a model she is careful with what she eats to ensure she maintains a slim figure. To me, this is a much better example of a model who makes the point that models shouldn't have to be super skinny to be considered beautiful. Those other girls need to take note.
https://au.news.yahoo.com/sunday-night/features/a/7391697/a-day-in-the-life-of-jessica-gomes/