The advantage of a salary cap is that it makes for a more interesting league. I think we all can agree the Premiership is the most interesting elite national league in the world. To me, this is a result of two factors: they attract players as good as any league in the world, and of the elite national leagues, the Premiership has the largest number of reasonable competitors for the league title.
La Liga sucks because in any given year, you know Barca or Real will win the league. There's only two intrinsically critical games per season in the league. Serie A is slightly better, because Juve, AC, and Inter can win the title in any given year, but no one else has threatened that aristocracy since what, the Maradona Napoli squads? In the Premiership, even in a top heavy season, four squads have a reasonable shot of winning the league. This year, I'd say seven squads can have dreams of winning the title that don't depend upon icy runways: the big four, plus Spurs, City, and possibly Everton.
In a draft league, every team will, over a relatively small period of time, have a shot at winning the league. To me, that makes for a more interesting league. If that comes at the cost of knowing the Arsenals and Inters of the world will always be better than the MLS champion in any given year, so be it.