Can't see any argument that the PL has more parity/competition than American sports. In 23 years you've had 5 clubs win the title: United (13), Chelsea (4), Arsenal (3), City (2), and Blackburn. The NBA--which has the least parity of the NA sports--has seen 8 clubs win the title in that same span: Lakers (5), Spurs (5), Bulls (3), Heat (3), Celtics, Mavericks, Pistons, Warriors.
Maybe if you want to extend back another 23 or 46 years you'll find more parity among top-flight English football, but at this point the question becomes absurd because you're comparing entirely different structures.