Stealth aircraft aren't supposed to be stealthy from all direction, I'm sure you know that. Even the most stealthy aircraft can be detected from the direction where it got strong reflection lobes.
In case of the F-117, it was tracked by a VHF radar, the frequency which it was not designed to be stealthy against. And when it was attacked, it shown the side to the battery, which if you looked at the scattering chart posted earlier, that where the RCS the highest
About RQ-170, it is a bit different from a normal stealth aircraft that it doesn't have pilot, it is an UAV, it might need constant transmission with the command center so it might be easier to show up on passive receiver. Secondly, as far as I know, they captured the RQ-170 by jamming GPS and feed it the wrong coordinate to land. That is much easier than to shot something down since you only need the general direction.
B-2 design was modified for low level mid way through development phase, for the fear that radar might advance too fast, they basically make a serration at the back. However, if you look at the design of B-21, you will see that it emphasize high altitude flight again and have pretty much the same shape as original B-2B-2 modified for low level penetration, trend towards stand-off weapons, autonomous jamming and unmanned aircraft, claims about counter-stealth US radars etc. do not reinforce the impression that US VLO works as claimed.
Recently instead of using Turkey's S-400 to show the world their superiority, they reacted in hiysteria at the prospect of those radars getting in close contact with the F-35... why not demonstrate they can dance circles around the system and ruin Russian reputation and their best military export item?
The trend toward longer range weapon is understandable, all thing equal, stay at longer range is more safe. However, apart from stand off range weapons, they also develop many mininature weapons for stealth aircraft.
Unmanned aircraft and autonomus jamming are necessary, because not everything should be done by stealth aircraft. For stand in jamming for example, you just want something cheap.
I don't see the introduction of low frequency "anti stealth" radar as the proof that stealth doesn't work. I see that as, because stealth does work, that why these stuff get developed. Let me put it this way: do you think anyone develop HEAT and Sabot round if all tank armor can be penetrated by basic rifle?
Yes their comments has been quite stable. On the other hand, they also developed quite a high number of "anti stealth" low frequency radars. If RCS of stealth aircraft are around 0.1 m2, I don't see why they need VHF radar to detect them. Even big fighter radar will track these aircraft from quite far, let alone big surface radar.> Russian position regarding expected RCS of Western fighter sized models has remained relatively stable through time in the order of magnitude of -10 dBsm. I don't know if it is right or what does it comprise exactly, but it has not changed too much over time actually, and it includes them operating in the same theater in Syria.
While Russia and Usa operating at the same time in Syria. Stealth fighter operate there always either carry external fuel tank or luneburg lens.