Well, I don't think the Spit XVI is best in any absolute sense.
True - its not the best plane in any absolute sense. However, the sum of its parts makes it what it is.
Consider, for arguments sake, that it doesnt do any single 'thing' as well as another plane in the set. The 190A5 can outroll it, the 109K4 can out climb it, the P-51D can out-zoom it, the P47D can out-dive it and the A6M2 can out-turn it.
The reason the 16 is so deadly is because it can do *everything* at 95%. Every other aircraft listed above has, with the exception of the positive trait mentioned, one or several areas of performance which are markedly inferior.
In simple terms, again - the 16 has no glaring weakness.
Pilots being equal, each of the above aircraft has a single tactic to employ against the 16 with a chance of success. The inverse is not so. The 16 has a myriad of tactics - many of which can be deployed at the drop of a hat - to counter any then current disadvantage.