US
strength: revolutionary, 90% of the time, first to do it
weakness: internal politics leads to delays and compromises

MIG-31 fly high and faster than US jets from primitive airfields. so how its not revolutionary. Revolutionary means that not easy to copy as it suppose to be so advanced for decades to come with no chance of airframes crack.

China
strength: industrious, fast to learn
weakness: started late

where you get this idea of industrious and fast to learn?. they have been flying jet MIGs since 1950s.

its natural

It’s not natural. China is simply more useful country to Russia.

They are not going to run out of money. Russia had highest reserves relative to population and debt.

Yes i agree. the J-15 benefits from China’s more advanced composite industry, allowing it to be much lighter and able to carry more than the failed su-33.
the pecking order for naval fighters would be
f-35 > j-15 > rafale > f-18 > F-15 Mig-29 > F-4 > su-33

There is no public success with major composite use in Chinese aviation industry. they can only use some small composite as bandage but it cannot change fundamentally aircraft capability.

http://aviationweek.com/awin/comac-abandoning-major-composites-c919
Comac Abandoning Major Composites For C919

Russia gained 10 million people from Ukraine crises. Those isolated cities in Siberia are for resource extraction camps or industries that need to be built near minerals or defence factories that need to be protected from commercial inflation. It is nonsense that those cities not produce anything.
All Chinese are fleeing to West. and china male-femal ratio is very skewed due to one child policy. China is simply not able to fund its retirees.
Even in Valdivostok the labor is from CIS countries and Koreans. China simply not have skilled labor left to work in cold climate.

https://www.nknews.org/2016/02/happy-north-korean-slaves-in-vladivostok/
Confident Northern workers speak openly in Russia, unlike their secretive counterparts in China

Given that shape is the largest contributor to RCS management, designing a twin seater would not be that hard.

There has just not been a need.

twin seat fighters are draggier and heavier.
put those requirement into 5G and the whole thing can become slower and shorter range.
5G need to design in way that tanker/AWACS support is at distance from battlefield(otherwise they are going to be shot down), miniimum use of external fuel tanks, supercruise at most altitudes.

Looks like A-100 has Radar and EO sensor on the bottom of fuselage to track ground targets

http://www.airrecognition.com/index.php/archive-world-worldwide-news-air-force-aviation-aerospace-air-military-defence-industry/global-defense-security-news/global-news-2016/september/2909-scale-model-of-russia-s-future-a-100-awacs-aircraft-spotted-at-army-2016-exhibition.html

This may also take the role of Tu-214R. This shows that transport aircraft is the correct approach to building AWACS.
commercial airlines too fragile to deal with 10 ton antennas and those heavy pods on the wings.

Given that the T-50 (a lot) & J-31 (just a bit) are larger than an F-35, they would have to actually have a better level of stealth technology than the F-35 in order to have better RCS values. Considering that these planes are their country’s & company’s first foray into the dark art of stealth tech, that is highly doubtful.

larger does not mean fatter. its a sleek efficient design. F-35 is as draggier as F-15/F-22.