Surprisingly, my CX were still moving pretty well at 12 weeks. They also had massive drumsticks and thighs to support those breasts. But, yeah, they are pretty freaky looking, and is one reason I've decided to go in a different direction this year. The slow broilers from this spring dressed out between 4 and 5.5 pounds at 14 weeks, so a pretty big difference. And, I really don't expect much over 3 lbs for a heritage cockerel at 14 weeks. So, it's going to be a trade off between having more active and normal chickens, and more butchering.
Growing up in suburbia, our backyard was devoted to growing fruits and vegetables. I really didn't appreciate it at the time, but it was a great example. We always had a compost bucket under the sink, so less garbage out on the curb.
I think if 1) people would use the resources available to them; and 2) try to avoid wasting so much food, collectively it would have a very positive benefit on food supply and the environment.