If you're only talking flints or percussion side hammers, I would still disagree, range within reason. However, if you include a modern inline, well, its very easy to send a 350gr or 400gr bullet at 2500fps. There's nothing in North America you can't hunt with that. Including all the large bears.
Some states allow smokeless muzzleloaders, with more and more states allowing them. You can send the same 350gr or 400gr bullets at 3,000fps.
Many African animals, including the cape buffalo, have been harvested with 50cal rifles using T7 pellets and heavy bullets.
You can kill an animal with a marble if your shot placement is correct.
Practice, practice, practice and practice more............