Really? How many times have you achieved #1 rank in a p51D? For that matter, how many times has anyone achieved #1 rank with the 51D as their primary ride?
The P-51D seems to be neither more nor less capable of achieving #1 fighter rank in it than many other LW Planes...
Good weapons, enough ammo for a lot of kills, decent views and enough speed to get you safely home most of the time, if you avoid gettign low & slow in a enemy rich situation
But now I got curious and looked up the #1 fighters from the last two years:
(First plane mentioned has more kills)
A very few times, there was some doubt about the true main ride for fighter mode when the culprit got actually most of his kill in attack mode. I such cases I selected the most typical "scoremonger" ride from the list. For example Temp & La for Pacerr... ,)