It seemed to me his criterion was to pick teams that were good now and had the financial muscle to remain good going forward. Only the Astros have a bit of a question mark about the second part.
We could have six "super teams" next year: the Indians, Yankees, Astros, Cubs, gnats and Dodgers. He didn't pick the gnats because he perceived (correctly imo) that they are stretched financially and their window might close in a year or two. Ditto for the Indians.
As a side note, the existence of these six super teams going into 2018 means that the remaining 24 teams are basically competing for the 4 wild card spots.