Apples to apples I agree with you, a lighter car can trap a lower MPH with a quicker ET. The first one to cross the finish line (the lower ET) wins. MPH compared to weight is a indicator of horsepower not how fast a car is in a race, ET is the indicator of how "fast" it is. 100lbs = 10hp in power to weight ratio. Even from a roll a car with a lower ET will beat a car with a higher trap speed, hp to weight ratio wins. Unless you are racing two cars identical the trap speed of the car in the 1/4 mile doesn't mean any thing but ET will no matter what.
I agree that the premise behind a 1/4 mile run is to determine which vehicle travels the distance in the shortest time.
What I don't get is why the the mph seems to be so difficult to get. It is a very useful performance metric. Look change it from mph to feet per second. 1 mph is equal to 1.466 feet per second.
100mph is 146.667 feet per second. 102 mph is 149.60 feet per second.
So what does that mean?
Well it means that if we continued at that same rate(no change in acceleration)at the end of the 1/4 mile that the car going 102mph is going to pull away 2.933feet every second they continue at that rate.
So now tell me why mph means nothing?
If it means nothing why is your stage 3 gti faster than my ko4 gti or a stock one for that matter? Cause it makes more HP (torque technically, but since hp isj ust torque over time we can cheat and call it hp)which is directly connected to the mph at the end of the 1/4. Regardless of the time it takes to get there.
Technically we could pick any distance. Its just that the 1/4 mile has been a performance benchmark for so long constants have been derived to explain this sort of thing.