Strong muscles require food, high agility is expensive, and while quick reflexes are great, what's the point if you can't coordinate them?

Humans most significant advantage is our ability to cooperate in an extensive manner, well beyond anything other animals do. Each human exists as a dual being; an individual and a team member, a node and a server. This is an underestimated advantage when most people think about it.

Say we are back before civilization. We are hunting Gazelle. I ask you to run ahead; you do so, we've had this hunt before, you usually run ahead. I take off after the Gazelle, ready to push it in to your trap. While you're waiting, you notice a lioness in the grass. You can choose to do a few things here, but the fact that you can make an individual decision, such as to kill that lion, while simultaneously operating within the parameters I set for you is fantastically useful in harsh environments.

Large brains let you plan, react, and fight better, and most importantly you learn from mistakes beyond simple responses. If you fight a lion and survive, you will know what not to do in a situation, and can then tell others what not to do. The best advice is not to hit the sharp parts.

Humans are also rather naturally talented warriors. Fight something anywhere and the first thing you'll do is pick up a rock. Its instinctive, and we know, without really thinking, how to hold that rock, how to hit best with it, and how to throw it. That's not a technological advantage, its a dude with a rock, and I'd bet on a hunting group of humans with rocks and branches against any other animal walking the planet.

Last thing before I sleep, you realize humans are probably the best adapted to harsh climates,right? Sure, if you take away our complicated technologies a good portion of people will die, but that'll happen with any environmental change. Humans have occupied the world in every corner that we could reach. Mountains, tundras, deserts, islands, forests, tropics, swamps, volcanic areas, you know it. I can't think of a species as universal, because unlike say, dogs, or livestock, all of the humans in the different areas are basically the same. Skin color changes, facial structures change, but there's no longer hair, no tail, no super elongated canines, nothing. its a bunch of humans. And we did all of that without a motor to drive us. Hell, most of the human race got to where it was by walking.

Sure if you have a lion bite us we get messed up, but put the lion in Siberia and it dies. Humans just make it a coat.