Different sports bro. You are comparing apples and oranges. One individual player has much more of an impact on the game in the NBA than they do in the NFL, outside of the QB. Most every other position is replaceable, which is why you don't see the same leverage/power.
What about the spurs than, they have a top 5 player leave, and still at the top of the western conference.
You can find anomalies and other randomness if you look hard enough, that doesn't change the overall picture though.
Plug and play