somewhat balanced by there being more than one best seller list in existence

Somewhat. Not much. There are books that spend months or years on the bestsellers (eg. Fifty Shades of Grey), and just one of these books alone will blow away an entire tenth of the entire pool for that bestseller list - and then there are the sequels or spinoffs or licensees of existing franchises like Star Wars or Star Trek or Dune or Twilight...

many with a smaller pool of candidates than the NYT list.

That's not a point in favor because it means that you will have a hard time getting into those pools. It's only useful if you know in advance that you can get into them.