You have completely skipped the stringent rules about the knife in your summary, so perhaps you are just not aware of it.
The knife must be razor sharp - the slightest knick renders it unusable. The knife must be drawn in a single motion, any hesitation, or pressure, while cutting makes the animal not kosher. The location of the cut is precisely defined.
All of the above are there to minimize pain, because the knife is so sharp the animal doesn't feel the pain, any pressure on the wound would also trigger pain.
> or only on the first and last one (kosher)
This isn't correct. Only one blessing is said, and not saying the blessing does not render the animal not-kosher. The blessing is about the shochet, not the animal. This is different in Halal were the blessing is the primary thing that makes the animal halal.
> whether slaughter can be performed by any believer (halal) or only by a specific priest (kosher, only Sachets (a type of rabbi) can perform kosher slaughter)
The shochet is not a priest. Being a shochet is 100% about knowing what to do, and 0% about any kind of special status. Anyone can be a shochet, including women. And you do not need to be a Rabbi, you just need to be trained.
> bolt pistol
A captive bolt pistol has an unacceptable high failure rate. You can NOT consider them more humane than Kosher slaughter.