The joint Indian-Russian fighter is an important innovation and combines the valuable resources of both of these large countries. Russia and India both have vast resources that encompass scientific knowledge, military know how, and natural resources. Combining the two countries resources is sure to produce a fighter that will be able to challenge American fighters.
Even if Russia partners with India, I don't think their collective technological knowledge will be a challenge for the United States. Russia and India will have language barriers and different methods of working so anything they come up with, the Americans can come up with something better to maintain their superiority.
There is no nation or combination of nations outside of NATO that could challenge American supremacy in terms of its fighter aircraft. Even NATO nations would be hard-pressed to create anything that could compete, were it not for American designs and information-sharing. Additionally, even if those nations were able to put together a fighter with capabilities similar to the Americans', they would not be able to make the same quantity of them.
It seems that the two countries had some conflicts in getting together to execute the Sukhoi. I'm pretty confident that even with the technological advances made by other countries, the United States can maintain air superiority. There are always exceptions, but we have one of the largest and best funded air military operations.