LOL about the cats
Large breeds are a trick, aren't they? When I had my first big dog, a Dobermann, I was counseled to feed her as much meat as possible early on, theory being she needed the protein, because large breeds grow rapidly and they need the nutritional support of high protein. She grew large, was the best dog I've ever owned, and died at the age of 5 from liver cirrhosis. It about broke my heart. I always wondered if I killed her by not feeding her a more balanced diet early on.
It is accepted truth that Toy breeds live longer than larger breeds, and that may be true, but is it because, as you point out, the large breeds are pushed to grow more, faster? Could be.
Danes, I've been told, die younger due to several factors, not the least of which is their hearts are challenged by sustaining a much larger body - yet I have not heard of Irish Wolfhounds dying at the average age of 7 ...