Your confusing the MiG-25 for the MiG-31. The MiG-25 was the one that was deeply compromised.
No, I am not.
The Belenko defection handed an up to date model of the MiG-25 minus the weapons... the result was the MiG-25s in Russian service immediately got a full upgrade of systems and weapons that had been previously delayed due to lack of funding... the MiG-31 was also given a full upgrade after many of its systems were compromised by a spy codenamed Donald.
We bash a lot the f35 here including me but US have spent a lot in stealth and are without a doubt the best in that field.
The fact that many of its serious faults are known and still accepted and yet it remains enormously expensive to both buy and to operate makes me think it is all a Soviet era plot to destroy the west... in many ways it is like a supercar... looks cool in pictures but a pain in the ass to actually own or use... small and uncomfortable... uses enormous amounts of fuel just idling, and way too much power and performance for any normal person to use safely on imperfect roads us mere mortals have to navigate every day.
IMO if they reduced the detection range of the f-35 to 10-20% of the detection range of a f-16 it will be a very hard target. S-400 still uses X band for engagement which is the frequency band the mostly affected by stealth. I wouldn't underestimate them. And they very well what level of stealth their f-35 has.
The missiles don't home in to the target from launch... they are launched vertically to start with so a target 400km is hardly going to be lock on before launch.
Pretty much any platform can detect the stealthy threat and pass the general location to the S-400 battery and a missile can be launched to intercept... instead of detecting the F-35 at 50km it might only detect it at 30km, but that doesn't matter much because until the missile gets its own lock onto the target it can be guided closer to the target using other information from other types of sensors including L band radar or even IR sensors.
Turkish and Indian s-400 won't be game changers at all.
If you don't have an IADS then the S-400 could be kept mobile and will always be a serious threat to any aircraft operating in the area... the battery could operate with radar listening only and receive target information from radar batteries nearby that are doing the scanning in whatever frequency needed to detect stealthy targets... but it is Americans that talk about game changers... but then they are the ones fixated with gender changers too.
Official story about the f-117 is that they downed it when it had opened its bomb bays and the p-18 detected it at short range, not that far away.
It can only carry two bombs and the bomb bays remain open for seconds each time so it would hardly be enough for a missile lock and a missile launch and a successful interception... imagine if it was really stealthy and therefore invisible... you 360 degree scanning ability with a radar means your radars are spinning... what scan rate for a conventional radar... 6 scans per minute? What are the chances of the bomb bay being open at exactly the few seconds the radar is scanning past... more importantly in an aircraft that should detect the radar and know when the beam is going to scan past... with a laser guided bomb you open the bay... release the bomb or bombs and close in a couple of seconds... surely you could time it when the local radars are not looking at your aircraft... because if they can't see you are there they wont be sector scanning they will be scanning the entire night sky so even from close range they wont know you are there... even if they have your precise flight plans it would not help much...
Example, a potato peeling capability of a soldier is very important in certain situations, but having superior potato peelers will not win a war.
Especially potato peeling machines that are 20 million dollars each... they wont win a war but they could lose a cold war based on economics...