I've heard certain types of radar can detect everything nowadays. Nothing is truly stealth and it's just a gimmick. This was from that guy who completely criticized the F-35, Pierre Sprey.
I'm not an expert. I really want to hear the opinions of experts on this topic.
You won't find these kinds of experts on this particular forum. Maybe go find an aviation or military specific engineering discussion group?
Hacker News is the worst place for this kind of topic. Have you noticed that no-one applies formulas and calculations of any type in this particular discussion yet? Physically you can calculate the radar profile of all of these types of planes, and there are engineering spec sheets (albeit some are classified, but there's enough data out there for educated estimates)
But everyone is talking in terms of "like a bird" or "almost like background radiation" etc.
I'd suggest going elsewhere to engage experts on this topic.
Sprey, for all his accolades is also the person who thought the F-15/F-14 were mistakes (the former arguably the most successful jet fighter ever created), and didn't want the F-16 expanded into a multirole fighter.
I'm not an expert. I really want to hear the opinions of experts on this topic.