I worked in several slaughterhouses while training. I’m more concerned about how animals are transported prior to slaughter than how they are killed. I think that’s the biggest animal welfare concern. The fact that there are fewer and fewer abbatoirs means animals can be transported miles and miles to be killed. Thankfully it’s now illegal for live animals to be transported overseas to be killed. This law only came into force a couple of years ago.
OP, the majority of halal slaughtered cattle and other animals are stunned before being killed whereas kosher slaughtered animals are never stunned. It isn’t the exact same process at all. The stunning is an important step in ensuring the animals die humanely.
One important thing to remember is that 99.9% of slaughtermen just want to get on with their job and process the animal as quickly and safely as possible. That means it’s very much in their interests to ensure the animals are calm prior to being killed and that they are killed as quickly and efficiently as possible. If animals are suffering and take a long time to die then it affects the meat. Meat is extremely valuable and businesses aren’t going to risk producing low quality meat.
I once saw a big cull cow that wasn’t killed instantly by being electrically stunned and came too as it was being hoisted. It was really distressed and thrashing around. IPicture how dangerous that is. The slaughtermen treated it very seriously.
All areas in abbatoirs (in England, Scotland and Wales ) where there are live animals and where animals are killed have to have (good quality) cctv that must be available for the independent veterinary offficer (employed by the food standards agency) to see. I know there will always be some rogue abbatoirs but most are well regulated.