Kristof Goovaerts , as I said, stealth has it’s problems and is not an invisibility cloak. However, a single indecent over the entire life of an aircraft does not suggest a trend. Lets apply the logic that you suggest to some other technology.
During the Vietnam war, WW2 ear A-1 Sky raiders shot down multiple Mig-17. Under your logic, this means that the basic technology of jet aircraft is flawed, because a legacy system won in specific tactical battles.
As far as the Russians working on counters to stealth, I’m sure they are. I am not sure if you have been paying attention though, but Russia pretty much ceased to be a functioning state for about a decade there in the 90’s. It is pretty impossible to undertake the kind of revolutionary research that is needed to develop a real ‘stealth’ defeating technology when you can’t afford to pay employees. Combine this with the fact that Russia lost huge amounts of the weapons industry it had built up to other nations (30 odd % to Ukraine alone), it is pretty hard to imagine that they have been able to put the necessary funding behind attempting to properly counter stealth.
What they have been able to do is continue to evolutionary develop equipment. This had lead to more effective radars and sensors. This are not magic radars that ignore stealth, and a stealth aircraft will do better than a non stealth aircraft in penetrating the airspace.
I hope that everything is doing well over in Olgino.