I come from Mennonites. Plenty of animals on the farm are allowed to live full lives. Anything doing any kind of work can be, which all animals on the farm are capable of. Milk and eggs don't require culling. Even layers past their prime will still eat pests and scratch manure into the soil and teach the young to do same.
The figures you quote are not for heritage breeds. They are for breeds which have been selected for extremely rapid growth, often to the detriment of the health of the animal (and presumably the person consuming them).
> the meat of a relatively old animal taste far from what people are used to eat and is (way) more expensive to produce
You don't get it at the supermarket, that's for sure. But I can get it at my local farmers market. You may be able to too. I would argue that it's entirely feasible, but depends on priorities. Most people prioritize profits, convenience, and speed.
Our poultry didn't last more than a year either, and we weren't factory farming. We bought 15 chicken every year, 3 male to eat before they were fertile early spring, 12 female that we ate during the next winter. And half a dozen rabbits too. Then my grandparents grew too tired and started to travel instead of farming/taking care of poultry.
The animals might have been happy (or, at least happier than in a factory farm), but clearly their life were short.
Joel Salatin practices the sort of farming I'm familiar with: https://www.youtube.com/@farmlikealunatic
This is what happy chickens look like: https://www.youtube.com/shorts/VHvDEzpD5es
and happy pigs: https://www.youtube.com/shorts/B6qk0IbCC5U
The figures you quote are not for heritage breeds. They are for breeds which have been selected for extremely rapid growth, often to the detriment of the health of the animal (and presumably the person consuming them).
> the meat of a relatively old animal taste far from what people are used to eat and is (way) more expensive to produce
https://en.wikipedia.org/wiki/Coq_au_vin has been the definition of a peasant dish for a century or two at least.
> but as some people point our frequently: we can't know for sure how another animal feels so it's only guess.
Anyone who's spent time with animals knows. As surely as you know if your dog is happy. People are the ones who hide their feelings.