Real-world traffic is displayed in the sim with a significant delay (relative to Flightaware/FlightRadar24) of minutes and in very few numbers.
RealTraffic & PSXseecon are able to display nearly all traffic in real time in P3D
Noticed the same problem, a flight in the sim only departs 5-10 minutes after the real flight has departed in Flightaware/FlightRadar
I have the same issue as well. Slightly annoying!
AI Traffic has been significantly improved in this area via SU11 and SU12.