That’s the case at my location. I was starting with a 3dB Antenna, went over a Jetvision 5dB and currently operate a 7.5dB Vinnant.
Before moving to Airspy and later Airsquitter i was using the blue FA stick together with the dark blue filter for 1090 MHz
By removing the filter there was not much difference from reception.
I was only able to increase gain to almost max without having an increased messages > 3dbFS
Number of positions and number of aircraft was pretty much the same, independent from which antenna was attached.
But it seem i do not have that much interference from other signals here.
And using AGC is never a good idea, at least not for the FA stick: