The U.S. is superior, yes, but that is because it did not have to go through the years of colonialism that China or India went through. The U.S. always had quite a strong manufacturing base since the 13 colonies era as well. US being the strongest may have been the trend for 200 years, but that is set to change, and has probably already changed. Even if 20% of India or China's population becomes an educated work force they will surpass the United States.
It took a long time for the roman empire to fall, and with the US having it's hands in most of the global financial and trade organizations and routes, it's going to take the US a very long time to decline in power. China and India have a very long way to go before they can declare themselves stronger than the US, and it's not like the US isn't making gains as well.
Buddy, a lot of things change in 100 years. Pakistan WILL NOT survive like this, hiding behind nukes for its survival. India's defense budget is rising each year and there will come a day where Indian defense budget is the size of Pakistan GDP. What will Pakistan do then? The best thing for Pakistan to do is quit the army and become a pacifist nation like Canada, Japan, or South Korea. Soft power!!
Of course a lot of things change in 100 years, but that doesn't mean reality suddenly shifts and turns negatives into positives. A hundred years is NOT a long time, that's a single person's life span, things won't change dramatically, when it comes to geopolitics.
You seem to have this idea that a large size is the end all be all, but it's not. In fact, there are a lot of reasons to believe that once Pakistan's gets it's financing in order, and finally contains the war it's fighting, it may very well surpass India's growth. Pakistan, unlike India, doesn't have the burden of a billion number population.
Also, Canada and RoK are not pacifist nations, both nations have a clear defense doctrine that dictates the use of military power to protect their nation's vital interests. Soft power is important, but it shouldn't be the only basket to put all your eggs in.
Finally, the day Pakistan quits the army and becomes pacifist, is the day India takes over Pakistan (covertly or overtly, take your pick). It's simply naive to think that Pakistan will survive if it's military is next to nonexistence.
But, I guess our great great grandkids will have to see how it all turns out. Will there even be a world in the next 100 years? Who knows.
Who knows, indeed.