Bengalis are the brightest folks, then why are you acting like a... well whatever!
What I am already finding too weird in this discussion is that people are comparing fighter jets without any idea of what they are meant to do ie their role. J-20 and J-31 are two totally diferent planes in totally different roles. One is a large plane initially meant for ground attack and deep penetration strikes and other is a mid sized plane.
Then again, US or rather any air-force flies planes in formation and mixes and matches the planes for tactical advantage. Heck! India in an exercises with the US had shown an interesting tactic of mixing Mig-21 with Su30MKI for great effect. Generations is more like bunch of features and different generations in different countries had different meaning!
Lastly, Stealth! everyone is so enamored by stealth! What they are missing is that J-31, J-20, F-22, PAK-FA are stealthy from one/few particular view(s) usually frontal and to few bands of radio energy. In a real war, you will not be going one on one and there will be fusion of radar information, radars possibly using different bands, not to mention with AWACS and perhaps sea based radar systems, if the theatre is in SCS. This is too complex and I doubt even the think tanks like RAND are capable of correctly predicting the outcomes, nevermind amatures. That said, there are very few countries that have more experience of war than US and Russia. China is still to prove her chops here.