The pistols are not necessarily any less accurate than a modern one, in my experience. But, of course, marksmanship with handguns at further than a few paces is often difficult.
I'd guess the big danger for duelists would have been damage to internal organs or deep wounds becoming infected. Bullets could do this, as could the smallsword, a purely thrusting weapon which would have been the sword used in the 18th century. McBane (https://en.wikipedia.org/wiki/Donald_McBane) wrote of the difference between cutting and thrusting swords "the smallsword kills, yet you might take fifty cuts and not be disabled".
If McBane was telling the truth he certainly managed to get away with a large number of duels, though.