Then who decides the purpose and which purpose is just/noble? This seems to be unanswerable since we do not have counterpoints by other species. By this same logic it wouldn't make sense for people to create offspring, nor would plants be serving a noble purpose as our food.

Regardless, in terms of humaneness, the aforementioned approach is a pragmatic step up from industrialised meat farming. Morally, however, the argument for killing an otherwise "healthy" animal regardless of the humaneness involved is specious at best.

I'm not sure that's a given. Animals aren't humans; they don't know what's going to happen to them. Is it really a given that it's morally worse to raise an animal on a small farm, have it live a comfortable life, and then eventually slaughter it for meat, than to have it never live at all?

"than to have it never live at all"

Please also evaluate this in the context of humans. Should it be allowable for humans to create offspring to satisfy their "need" to reproduce then it means their offspring have to suffer working and struggling, likely without a noble purpose?

I prefer living to not having lived. I would expect the same of most people who aren't struggling for the necessities of life. About the only seriously negative thing about it in my experience is contemplating it eventually ending. And animals don't have that, as far as I know. So I'd think an animal life largely free of pain or suffering would be a net good.

I feel like our purpose is just to ensure continued existence of our species. Anything that happens between when you were born and die are just steps to ensure you (or your kinds) are worth keeping around, ensuring the continued existence of the species.

Animals are not Humans. They don't have the mental faculties that allow thinking about "purpose". The animal is satisfied as long as its needs are met, and not living in agony.