Also, sort of like today in our lives.
A normal person is not going to go toe to toe with a Bear (or perhaps even an angry horse that cannot be calmed). Even a spear in hand will probably have that fight go somewhat badly for the human.
Human's are successful (even with primitive weapons like spears) because they work in groups and work together with tactics and strategy. It's not just one human vs. that Bear coming into their village, it's a dozen or more humans verses that bear...all armed with bows and then with spears if that doesn't take it down.
Sometimes the bear wins, but in the larger groups, normally humans can win.
Of course, this doesn't work as well against Orcs, goblins, or others who also congregate in large groups. These are fantasy groups of course. The only advantage humans have is higher numbers in this case...and of course...Heroes (and that's where the PC's come into play).
We have one other advantage today that gives us a better hand up than they did in primitive times. Technology. Technology is a game changer.
Mankind's biggest weapon isn't ability scores, hitpoints, or class levels todays...but our brains which help us overcome enemies, animals and the environment.