Lushe,
Ignore Krusty. He is on his daily Spitfire Hate.
Ignore Karnak with his narrow mind.
Substitute spit for whatever, the example still holds true. Newbie comes into the game flying what he thinks is a great plane, gets killed repeatedly by other newbies, moves to "ride X" (which in 90% of cases is a spitfire) and finds out he can now get the same kills as they can. End result: N1k2 "George" gets flown less.
I don't think the N1K2 is any less effective than it used to be. I landed 10 kills in it after it was remodeled (all bombers). However, the La7 and the Me262 both got nerfed a bit (the 262 a lot), so while there may be performance reasons for their decline, I think there are other reasons at work with the N1K2.