GR, you are correct. I was mistakenly under the belief that Earths atmospheric volume was limited by the escape velocity of atmospheric molecules. In fact, on Earth, this only happens to Helium and Hydrogen. Earth is capable of supporting a much larger and denser atmosphere.
I have just learned something.
So yes, I believe MSL pressure is increased proportionally by the weight of all airborne aircraft (and birds)
As an aside, I believe the water pressure at the bottom of the ocean also increases for every floating vessel, but in this case it is not proportional to the weight of the vessel, because the ocean walls are not vertical.