Like you say yourself, stealth isn't a binary thing, but rather a set of techniques to reduce the detection range. You can be assured that Russia and China are

Like you say yourself, stealth isn't a binary thing, but rather a set of techniques to reduce the detection range. You can be assured that Russia and China are working hard on technology to detect stealth planes (e.g. multistatic radar systems). But again, it's not a binary thing. Even with a multistatic radar setup, a stealth aircraft will have lower detection range than a non-stealthy one. And considering both China and Russia are developing stealthy aircraft like Su-57 and J-20, it seems they themselves are not thinking that they have the magic technology that would make stealth obsolete.