The truth is, if Barca or Madrid were playing in Serie A, they'd win it at a canter, perhaps not 21 points ahead of a 3'rd placed team, but at least by 10-12 points from their nearest rivals. They are just that strong.
Serie A seems more competitive because the current teams of Milan, Juve, and Inter are not as strong or as balanced as they used to be. Our current Juventus team, as much as I'm happy that they are leading the league, would probably finish 5th-7'th during the heyday of Serie A between 1988 and 2001.