Well-understood and said!Don't forget, rear ride height also changes a lot of dynamics of the bike. Raising the rear transfers weight from the back of the bike to the front, and also impacts the bikes attitude, and thus the aero of the bike as well as the turn-in feel of the front end (rake and trail).
Suspension has to be looked at as a whole system. One small change impacts many things. Rear spring preload most certainly changes ride height, but it changes other things too. It changes the range in which the shock is working, as well as where in the travel range the rear shock linkage is operating. The goal of setting sag is (generally) to get the rear suspension compressed about 1/3 of it's total travel. This leaves headroom for it to extend on rebound but not compress it so far that it runs the risk of bottoming out. The Gold Wing does not use a rising rate rear linkage, and is fairly linear though out its range (except at the very end), but some bikes do, and this also has to be considered. Changes to the front suspension can also impact ride at the rear, and vice versa. Tire pressure also plays a roll, as does the stiffness of the sidewalls and type tire being used.