I was under the impression that the U modes were just saveable modes for the rider to select.. as if you make a change to A, B or C modes they will revert to factory settings after you cycle the key… U modes won’t unless you do the factory reset…
I was under that impression also but the bike just didn't feel fast in A mode so I started messing around and looking at each setting. If they aren't off then the computer is still reducing power in some form. It's not nearly as snappy as the U setting with everything but the QS turned off.
On a roadcourse you may not be faster but for those at the dragstrip or doing top speed runs you want every bit you can out of it until the ECU is unrestricted.