This is a good point. You don't create an aircraft more powerful or capable than it needs to be top achieve its goal. With the issues the Russians are having with the Pak 50 it's likely there will be no non-USA 5th generation jet in any great numbers. So why would you waste billions when 4.5...
I'm not sure there are usually 2 superpowers in the world, the situation with the Soviet Union and the USA was the exception.
To be a superpower after all you need pre-eminence which precludes there being a peer competitor around.
The definition of a superpower requires also world wide power...