Hello - if we think in that mode so there it cannot be build any stealth aircraft. SR-71 was stealth for MiG series from that time.
B-2 F-117 F-22 F-35 are stealth for other aircraft (MiG-21 23 25 27, SU-22 etc). I didn't write MiG-29 and Su-27 family because of their Bars - it is thought it can track stealth aircraft.Mikhail Simonov think Su-37 (or almost Su-35) is fifth gen.
Think about palsma shield - reduce up to 100 times RCS.
Think about T-95 (only prototype). Think USA want to reduce its M1A2.
Think about Topol-M, Bulava, new subs (2 at number) Borey class (a new class). Can US to response to Topol-M?
Russia must spend more money to destuction of sub that are not used, chemical weapons and ICBM that are at the end of life. But russians are smart - they ask money from Japan and Western countries for that, but they used their money for tech.
Russia help arab world to put fear in U.S. people.
Again at aircraft - why USAF bought MiG-29? If MiG are weaker than Fs so they don't need to see what MiG can do. (USAF bought many MiG - only from Moldova 8).
Think about defense. S-400!
Have US a missiles like S-400?
There are many aspects where USA are behind Russia.
Russia sell equipment to NATO countries!
I read once Russia in future want to sell even aircraft to NATO countries!
About Su-27 vs F-15.
In real world, yes, they didn't fight. But in Cope India USAF lost.