I guess the engineers knew what they were doing when they picked the size of the tubing for the autolube. I can easily see how if you went up to a larger tubing, air would stay in there and it would be very hard for it to fully prime to the point where it's pure oil.

When I read about the issue of bubbles in the pump outlet line I remind myself that the end of the line opposite the pump is connected to the intake track of the engine. So the line is "seeing" the positive and negative pressure pulses of the engine. The line is likely contracting and expanding with each revolution of the engine. The softer the tubing is the greater this effect would be.