Given the climate of our world, we have a certain amount of arctic tundra etc. The best way to extract nourishment from that is foraging by e.g. reindeer. That holds irrespective of the population density.
Also, reindeer is one of the most ethical ways of modern husbandry. Animals live out in the wild, supported by humans e.g. adding feed when there is little to eat, protecting them from carnivores etc, and then they are slaughtered in a sustainable way after living close to how they do in their natural state.
that is a very long chain of ifs, any of which can evaluate to false
EDIT: there is also no precedent for what you propose and if we go by the partial match of grass-fed beef, the yield will be so small compared to the population as to be pointless
There's almost 2 million domesticated reindeer worldwide, compared to 1.4 billion cattle, so it's tiny for sure. But in most of those regions, it's regulated such that only first people/native inhabitants/etc. are legally allowed to work reindeer.
how do you propose the mindset and techniques behind first people's husbandry sustainability can be scaled and applied to profit seeking "modern" farming?
Also, reindeer is one of the most ethical ways of modern husbandry. Animals live out in the wild, supported by humans e.g. adding feed when there is little to eat, protecting them from carnivores etc, and then they are slaughtered in a sustainable way after living close to how they do in their natural state.