No, MPG more easily answers "how far can I go on the gas I have?" Gallons/100m more easily answers "how much will this trip cost me?"
But, as you have both pointed out, it will is not the best figure to use to make optimal decisions about minimizing my fuel consumption and carbon footprint.
Both of which are equivalent to "how much will this cost me?"
How do you figure? If I want to drive 65 miles, and my car gets 30 MPG, I know it will take a little over two gallons. Doesn't get much easier than that.
But to use the 3.3 G/100M figure, I have to first figure that 65 is .65 of 100 and then multiply 3.3 by 0.65. All this gives an accurate figure, but I find using the MPG better for arriving at the "a little over 2 gallons" result.
Your milage may vary, of course.
But my larger point is that one type of measure will predominate in the USA and another in Europe, because Americans and Europeans think about things like consumption differently. This does not mean that the US system is "stupid". It just means that Americans don't choose to be straight-jacketed into European rationing-based thinking.