When you take a high satiety, high fat item, and replace it with a non-fat, low satiety item, you are in effect replacing fat with sugar, because you will eat/drink more of it to get same number of calories, and same amount of fullness.
You are making an argument that people do so, do you have any evidence for this ?
There is a negligible difference in glycemic index / glycemic load between the variations of M.F. milk products. Some analysis has skim milk as having a lower GI.
Unflavoured Milk is not relevant to the GI conversation.
Ok, there's no different.
Beyond that, Minor differents in glycemic load are irrelevant if you're consuming milk with a meal, like the kids in school are doing.