I think something such as quality of life, standard of living, etc. is also a very appropriate way to compare the relative prosperity of various countries. Yes, India and China amass a large GDP because they have so very many people. But if you look beneath the top layers or classes in those countries, the average Indian or Chinese does not live a life comparable to their counterparts in the West. I think the large populations of such countries are a hinderance as well as a help. So long as China and India have such huge populations, they will struggle to provide sufficient food, water, medical care, shelter, education and social welfare to lift the standard of living of the bulk of their people. I don't think you can really say a country is prosperous if the average citizen is in a struggle to obtain life necessities.
Are India and China improving on that count? It appears so (more so for China than India). Maybe, as Nat stated, the improvement in wages in those countries may not only help their people, but it could also help stem the tide of job losses in Western countries.