To even pose the question of animal suffering is unique to humans. After all, it's only humans who create humane societies to advocate for animal welfare.
Why?
I don't know how others belief systems would explain that, but from a Christian perspective, humans aren't exactly the same as animals. We're like animals in that humans and animals are all creatures, and yet distinctly non-animal in that we're the only creatures made in the image of God, and given rule over all creature to promote the flourishing of life---human, animal, and plant---for God's glory. And the biblical story is that humans went so far off-course in rebellion against their Creator God that the Son of God had to become human, die, and rise again to restore our ability to care rightly for creation.
Thus, concerns to minimize animal suffering are uniquely human concerns because we /aren't/ animals, but human; and the concern itself is proof we're different from other animals.
Many animals are perfectly capable of understanding the suffering of other animals. It's illustrated by menu recorded instance of one animal helping other animals in need. Even of a different species. There's probably nothing unique about humans except slightly nimbler neurons.
As for the stories humans invented to explain their grace and their horribleness I can't say much. Only that we are very creative in that regard.
I think anyone who’s been in a slaughterhouse would find it difficult to agree with that statement and even so, the sheer scale means that the amount of suffering is unfathomable.
Not to mention the terrible conditions that animals are forced to live in and injuries caused by processing (from birth to death) [1] as well as abuse by low-paid workers who are, themselves, working in poor conditions. [2] Factory farming is not clean and free of animal suffering by any means, but most people's experience with animals as food comes in neat, little, clean plastic-wrapped chunks of meat.
Sheep are stunned and are pretty much out instantly.
IDK if you've ever slaughtered a sheep the non-slaughterhouse way done where most of the people live (i.e. the third world). I've done it out in rural asia. You take a long blade and pierce the heart / surrounding blood vessels straight through the chest. It takes a second or two for it to pass out. The slaughterhouse is a slight upgrade with basically no suffering at the time of death as they're instantly knocked out by electrical impulse.
If I were the sheep I would definitely pick the slaughterhouse over being shipped alive to the average end customer which is someone in the third world with a long blade.
Without cotext sure, but if you could visit places where people prepared animal for cosumption over last few thousand years. I'd say there is a trend expressing the intent of reducing suffering.
Temporarily putting personal feelings aside, I think you've touched on interesting philosophical questions: can something so subjective as suffering ever be fathomed, does it scale, can you do math on it...
I think the complaint here is not about the moment of death, but about the literal lifetime of torment and agony leading up to that moment. Death probably comes as a relief for animals raised on factory farms.
