Norris
did win his fight in every way (he gave up on taking out Shiro because he didn't want to sadden Aina), he fully accomplished his goal, which was to take out all the Guncannons. From the very beginning he had fully acknowledged that he most likely wouldn't be able to make it back to the base and would die. Survival was never his objective.
But remember that the Gundam used in 08th MS team were semi-mass-produced versions, thus they were much weaker than the Gundam RX, so it's not like Norris took on three actually over-spec Gundams. Of course, this doesn't change the fact that he totally whooped the 08th MS tem's ass, either.