Most sports with league play will have relegations and promotions, which changes the dynamics a lot. This makes for way more interesting games IMHO, but there is no doubt the draft, the salary cap and all that have led to US pro leagues being a lot more unpredictable in terms of who can compete for titles (not that salary cap, draft, etc could be done in e.g. international footb^H^H^H^H^Hsoccer, where it's totally unrealistic to have common rules like this in place worldwide).
It's also led to a mentality where regular season success is of limited interest, and combined with _way_ too many regular season games, it's not a recipe for success in my mind.