Damn, a world of magic, with technology advanced enough to have cannons and rifle guns, yet they haven't even come up with the guillotine yet? Still relying on the executioner to use a sword or axe up to that point? And they call this a 'humane execution device'?
So would the iron maiden, wooden horse, brass bull, and the stretcher be 'inhumane execution devices' in their world?
Guillotine was invented irl cuz it was considered more humane. Its inventor strongly opposed to death penalty and wished to abolish it, but there was no stopping the revolution, you see, thus Guillotine was invented to, well, reduce the suffering, I guess?
Remember, not only humane, but also efficient.
Idk much about execution by firing squad, but that type of execution is carried out by multiple shooter but only one has live rounds (at least nowadays, idk about back then), apparently to alleviate the guilt as the shooters wouldn't know whether they shot a live round or not. The guns here utillized mana, not bullets, as far as I understand it, so the benefits of using firing squad is not much different than straight up using axe or guillotine. Guillotine is also especially easy to use, even a child should be able to use it, as opposed to firing squad which must be capable to accurately shoot the convicted's heart with a rifle and I heard shooting a rifle accurately is much more difficult than shooting a pistol, but I don't know since I never shoot either.