Yup, the numbers prove the point that the best arena aircraft are not necessarily the ones with the most use or the most kills. In this case, love of the P-51 is the explanation for what we see. Except for hauling ordinance, the 190D-9 is clearly a better aircraft below 20k ft for the kind of fighting you do in a P-51, but people want to fly a P-51 regardless.
The 190D-9 accelerates better, climbs better, rolls better, has more firepower, and is faster below 20k ft than a P-51. Come to think of it, the only reason the 190D-9 should have a higher ENY than the 51 is the lack of a/g ability and flight time.