The Noll-Scully measure captures how far a particular sport or league’s distribution of wins deviates from a purely random outcome of wins and losses. Thus a Noll-Scully equal to one would be one that is purely random. Since the 2000 season, the average Noll-Scully in MLS equals 1.294, which is more competitive than the National Hockey League, the National Football League and the National Basketball Association.
(If you are interested in replicating these results, I got the data from MLS website and here is a step-by-step method to calculate the Noll-Scully measure of competitive balance - where I used the trinomial method under a standard deviation of the population. I also used the probability of a tie to be the actual yearly average of games that were tied).
Here is a chart of how competitively balanced Major League Soccer has been since 2000.
For those interested in replicating the numbers, here is a table of the results.