THRASH99,
I have no idea who you are as you are new here. Thus far you have been egotistical and often in error. While Ack-Ack is knowledgeable, he is not the foremost expert on WWII stuff here, however he is correct and you are incorrect in your claims about both the P-51H and the Spitfire Mk XVI.
First, be aware that the Spitfire Mk XVI is nothing more than a Spitfire LF.Mk IXe with an American built Packard Merlin 266 instead of the Rolls-Royce Merlin 66 in the LF.Mk IXe. LF.Mk IX first entered service in mid 1943, LF.Mk IXe, which changed the four .303s out for two .50s and added the capability to carry a 250lb bomb under each wing, entered service in early 1944. The Spitfire Mk XVI entered service in mid 1944, but other than the engine it is identical to the LF.Mk IXe and in performance both are the same as the LF.Mk IX from mid 1943. You are, essentially, up in arms about a fighter that was in service from the middle of 1943, prior to any Merlin powered Mustang and with a total production of over 5000 airframes.
So, do you think that Spitfire Mk IX/XVIs saw much combat between July of 1943 and the end of the war?
As to the P-51H, it was not used in WWII and was determined to be unsuitable to combat due to fragility and thus was not used in Korea. You are equating a P-51 that never saw combat with the most produced version of the Spitfire.