robin,
In heavy winds you're right, but in light winds, with no windsock, into a very short strip GPS groundspeed is very useful. It is. One of the fields I take the cub into is 240m with an 8-10 foot hedgebank at either end. In that context, 5mph of wind is significant, especially if it is on your tail. Judging a light breeze like that is not easy, at least I don't find it so and certainly round here local wind direction is very variable. Many factors dictate whether an approach will end up in a good landing and wind direction and speed are critical. The more marginal the situation, the more critical is the wind and the more useful becomes GPS groundspeed. By choice, I wouldn't do without it.
This all relates to low land flat field ops. If you are in the mountains, then the wind issues are different and runway slope will dictate approach speed and ultimate stopping distance.
QDM
P.S. Real Supercub pilots would think me a girl's blouse for saying that 240m is short!