A captive bolt does not always work on the first try, and it doesn't always fully stun either.
You can't just increase the power of the bolt or you get brain matter mixed into the meat, raising the risk of mad cow disease. So you have to carefully tune it to "enough to stun, not enough to kill". It doesn't always work.
With Kosher slaughter on the other hand making sure the animal dies very fast is important otherwise the meat is not kosher and can't be sold.
Consider this: When you use a stunner properly, the animal feels a split second of pain before becoming unconscious. At this point, pretty much every vet would say it can't feel pain.
But if you cut its throat while conscious, it can feel the pain of the wound immediately, and continues to feel it until the brain starts shutting down. This can take minutes. Cutting the throat does not cause immediate unconsciousness, and this is the problem.
Compare a properly stunned animal vs. an animal whose throat has been cut by via sechita, and tell me which one reaches unconsciousness faster. Because that is the animal that endures less pain in death.
It takes a few minutes for it to die, but it's totally unconscious for that time.
And I prefer to look at actual usage, not perfect usage.
For example: http://dx.doi.org/10.1016/j.meatsci.2008.07.016 for this type of animal 53% of the time the stunning did not work properly.
And according to http://www.viva.org.uk/campaigns/slaughter/std4.htm 5-10% of captive bolt stunning does not work properly. There are plenty of other sources that say the same thing.
No, it isn't. You tried to go on about ritual slaughter of animals, then backpedaled as your ignorance was pointed out. Now you're trying to reduce the issue of cruelty to animals in a slaughterhouse to a question of consciousness at the moment of slaughter, ignoring the fact that kosher laws require better treatment of animals than the civil laws governing slaughterhouses. The "we stun them, so they don't suffer" line is a favorite of the meat industry, even if it doesn't always work out that way.
But then, cruelty to animals isn't your concern. After all, it would be most humane not to slaughter the animal at all - but conspicuously, you're not arguing for vegetarianism.