Unless you are willing to accept that 'this is the way it is...', then take a trip to your dealer, and ask to start up another vehicle, put it in gear, and observe. If they both perform the same way, then that may be the nature of the beast.
But I don't think so.
I have read about how the motor mounts can be un-equally loaded, or distorted due to 'things' happening while being assembled. No idea what, but I can imagine if one mount were tightened while the others were loose, then the engine and transmission had to be levered into place to get the other bolts to line up, there would be uneven load on the mounts, possibly transmitting more vibration to the chassis than intended. There is a procedure that supports the drivetrain, loosens all the mount bolts, and then, with the mounts 'relaxed', re-tightens the mounts. That would make none of the mounts pre-loaded, and give full normal travel to all the mounts.
When the transmission is in neutral or in gear, the engine rpm should be maintained. Same thing when the A/C is engaged. If the idle rpms are not constant, there is likely a problem with the IAC or learned settings.