Any radar that can see F-22 or F-35 will in turn be visible by them. It will be a cat-and-mouse game. In which case training, doctrine, improvisation and quick learning matter a lot. Weapons may be expensive, but training is expensive too. Expenses aside, how can Russia train to use its S-500 against US stealth jets? Using what jets as mock F-35's? Conversely, the US can very easily train against a simulated S-500 battery. It's not like S-500's radars are some big secret.