Actually I talked to a Tesla rep managing one of the Supercharger locations. He confirmed that the charge rate is throttled by Tesla based on how much you need to discourage folks from topping off. According to the rep, if you only need 50 miles the car will charge super slowly, where as the rate for folks showing up needing hundreds of miles will charge almost up to the max 370 miles per hour. So not sure that's a good indicator, plus if Tesla can software limit the battery, they could also easily simulate a 90 kWh battery even if physically 100 kWh was in there.
Not saying you are wrong, it's anyone's guess, just not sure of the reasoning.