Assuming you installed the lightweight version of the GSX jetway replacement files, GSX is not adding any more objects other than the ones actually servicing your airplane, because the lightweight jetway replacement files contains the EXACT same number of object as the default, since one jetway is replaced with one jetway and one jetway link/bridge is replaced by one jetway link/bridge.
Even "Living World" vehicles or "Airport Service" vehicles that has been replaced in *appearance* only by GSX, haven't increased their number compared to default, they just look different. If you disable GSX Airport Services on a certain airport, you'll get the same number of default ground vehicles there.
Also, this would only matter IF you are on an airport with jetways replaced by GSX. If the airport is Disabled ( any 3rd party airport should ) from Jetway replacement, having installed or the Lightweight version of the jetway replacement files won't matter anymore, if the airport is disabled.
When GSX is servicing the airplane, it's likely the highest number of objects is reached when Boarding/Deboarding passengers, but you can control that with the Passenger Density slider.
And of course, if you are using an AI traffic product, you can ALSO control the overall number of objects in the scene by lowering the number of AI generated.
I don't think there anything we can do other than what we already did, by offering the ability to install a lightweight version of the jetway replacement file, and of course the Passenger Density slider which has always been there. ALL our objects are heavily LOD-optimized and 100% conform to LOD standards following the direction of the official LOD diagnostic tool so, from our side, we have done everything to be sure the impact on the system is as low as possible and follows all the known standards.