47 years (almost half the 100 years you're talking about) have passed since the Mets rolled in.
It boils down to winning. The figures clearly show (aside from the early years in Queens) that whichever team is winning gets more fans.
1962-63 The Yanks outdrew the "NL Town" and they went to the WS both years, losing the one in '63.
Shea opened up in 1964 and the Mets outdrew. The yanks lost the world series.
1965 - 1973 saw the Yanks finish 6, 10, 9, 5, 5, 2, 4, 4, 4 while the Mets finished 10, 9, 10, 9, 1, 3, 3, 3, 1 with a new ballpark and 2 world series appearances during that time. Mets outdrew during this time.
1974, 75 they shared Shea. The Mets outdrew in both seasons (probably because no Yankee fan wants to actually go to Queens)
1976-83 the Yanks outdrew. Renovated Yankee Stadium, 5 playoff appearances and 2 world titles will do that for a team. The Mets, meanwhile, never finished above 5th place (aside from 1976 - 3rd).
1984-92 the Mets outdrew. The Mets finished 2, 2, 1, 2, 1, 2, 2, 5, 5 while the yanks finished 3, 2, 2, 4, 5, 5, 7, 5, 4. 1 world title in 2 playoff apearances in Queens. No playoffs in the Bronx during this time period.
1993-present the Yanks have dominated in attendance. 14 playoff appearances compared to the Mets showing up in October 3 times. No world titles for the Mets and 4 for the Yanks.
So since the Mets came to a town that was apparently starved for some NL baseball the Yanks have 2 more years with higher attendance (if my math is correct).
The years the Mets were winning more, they drew more and the same can be said for the Yanks.
Thus proving my point that New York is not an NL town but rather they go to whichever burough is fielding a winner.
We can look for Brooklyn Dodgers/NY Giants figures and compare those to the Yanks figures later on. You may actually have an argument there. But we'll see.