It is less painful than execution by Firing squad, electrocution, hanging, or lethal injection. It is why it was invented....to shorten the “discomfort.” Frankly, if we are going to go back in history, why not bring back “Drawn and Quartered.” THAT would be fitting for terrorists.
By the way, the last guillotined person was executed in the 1970’s. Not that long ago.
Now that you mention it, the 1970s were sort of medieval.