In term of killing power the USA is top dog very much the way Great Britain was top dog at the end of the 19th Century. Great Britain ruled the seas with super battleships not knowing that the coming of the airplane capable of dropping bombs and torpedoes was just around the corner. Also not knowing that the submarine would soon become a practical weapon of war. All that money and man power spent on these super battleships would mean nothing come WW1. How many times did these super battleships come out to play? Only once in the battle of Jutland. Before WW1 Great Britain had also exhausted herself, resource wise, on small wars.
America has all these atomic weapons, nerve gas, deadly bacteria, etc but doesn't dare use any of it for fear of starting a major war where even the winner is an el supremo loser. Has the USA in the 20th going into the 21st Century spent a LOT of money and man power on weapons best never ever used? You bet. Is America right now exhausting herself on small wars? I would definitely say this is the case.
Do we think of super powers in a different way than in the past? Many of us do. The USA became a financial super power after WW1 because the USA entered into the war late and hadn't exhausted her resources like Great Britain, France, etc. Right now countries such as China have been at peace long enough to have built up their finances. India still has a way to go before it becomes a super power financially or otherwise but it is on its way.
In terms of population growth the USA shouldn't want to compete with China or India. China's population isn't growing as fast as that of India and they are over the moon glad of it. Numbers means very little in future warfare or future financing. Having the right ideas and the right hardware counts for so much more. The Chinese have this understanding. The Japanese have had this understanding for even longer.
My thoughts at any rate.