How about getting some stats on total # of players playing and then compare it to the data of the N1Ki....................... 
Why? The idea is to show proportion, not absolute numbers. But based on the K+D in the arenas there's fewer people in the arenas in the fall than during Summer. Now, that would make me say "aha!" about the N1K, "it's a squeaker ride!," but it's K/D goes down too, which is the opposite of what I'd expect once all the squeakers are in school, i.e. lots of noobs flying it who don't know what they're doing brings the K/D down.
Fow now I'm sticking with the Update explanation: some small changes have been made that make the N1K slightly less competitive, just like the La-7 and 262.