You have two types of muzzleloaders, traditional and in line.
Traditional is the Hawken style, or the Ky. long rifle. Usually guys do not scope these. Most guys shooting traditional won't shoot game past 100 yards. Up to that range these are very good game killers.
In lines are almost always scoped. With these you can reach out to 150 yards. An inline with a scope is just as good as a modern centerfire on that first shot, within that range limitation.
In deer hunting, one shot is usually all you get anyway.