If not, the best marksman can lose because the arms he's issued may not shoot the issued ammo most accurate.
A few years back there was a show called "Top Shots" where they claimed to be looking for the "best shot" and all the contestants were good shots, one could say they were marksmen.
However the way the show was down there was less marksmanship and more "luck" involved than anything else.
The guns were supplied, as was the ammo. Each shooter got a few shots to familiarize themselves with the gun, but were NOT allowed to adjust sights or otherwise sight in the guns for themselves.
So, literally, the shot going where the sights were aimed was a matter of luck of the draw. Close was common but being right on was not something you could count on, and right on for one shooter could easily be just a bit off for the next. Targets were mostly reactive, lot of fun watching them break but also seeing shooter just barely miss the bottle due to lack of being able to sight in the gun for themselves just put the lie to "marksmanship" being a factor, in my view.