A better trigger will help nearly everyone shoot better. The top competitive rifle and pistol shooters in the world, in multiple disciplines, ain't running stock triggers, and they have superb trigger control.
Yes, a very good shooter with good trigger control will shoot well with just about everything, but will shoot better with a better a trigger. Better can mean multiple things. I can take a stock 1911 and shoot a superb group at 15 yards with. I can have a good trigger job done on the same pistol, and shoot just as good a group, or better, FASTER. Faster, with equal or greater accuracy, = Better.