I really have no clue if or how it's working atm. I fly gliders almost exclusively, but wanted FS Traffic to have an imemrsive, realistic radio traffic.
In the twoo weeks I now own and use FST, I've heard maybe a total of dozen or so aircraft of airlines, usuallly KLM or Lufthansa, when tuned in on busy centers like Zurich, Milano, Marseille, Vienna. All the rest are "Generic" XY, which I asome are actually other online players.
I also see the occasional contrail, maybe 5 or so during a one hour flight. Never saw more than two contrails at the same time, again in areas which should realistically be very busy.
For me that just seems like FST doesn't populate the skies around me at all. If that's an error on my side (even though I adjusted my settings as proposed) or a bug, or wrong expectations, I do not know.