Big markets and cable TV killed the Celtics. They've managed 1 championship in the big market era. The NBA has a phoney soft cap which benefits LA and NY. The Lakers have benefitted living miles above the cap, but the Knicks haven't--from incompetence.
In baseball, the Yankees were gifted with a championship team in the 1920s, courtesy of Harry Frazee who generously sold them the core of the Red Sox team. But the Yankees continued to dominate thru the 30s, 40s and 50s, thru the strength of their farm system plus excellent trading. They then went into a fall when Mantle retired. Free agency in the late 70s was made to order for them and new owner Steinbrenner, who vacuumed up every free agent in sight--pushing prices up for everybody else. This was when Boras was still in his crib, or maybe studying business somewhere. Recall that's when Haywood Sullivan rebelled against FAs by "losing" the contracts of Fisk and Lynn. The Yankees then dominated with a largely mercenary team. Then, as I recall, Steinbrenner got prosecuted for some shady doings, expelled as Yankee owner. The team was taken over by CBS, which promptly tanked them by cutting their purse strings. King George ultimately got reinstated, and went back to buying FAs again, but this time the farm system was also contributing the likes of Jeter, Posada, Pettite, Rivera,etc, and the Yankee dominated again in the 90s and early 2000s. But they are in trouble now, because they are loaded with big contracts of aging players and the farm system is barren. The Red Sox, on the other hand, are World champions, with a nice blend of prospects and free agents. Though it seems they still wrestle with the dilemma of giving prospects an opportunity vs signing free agents.
How did I get into all this? I don't remember.