What makes it so matter of fact? Barca are clearly the better team now, have similar if not bigger crowds and get more media attention around the world. If we're talking about past accomplishments then you're as well throwing in names like Liverpool and Ajax.
Not even the biggest team in Spain
Trophies, players, name value, record in Europe and in Spain, etc. Ajax, Liverpool, Bayern, etc, are huge clubs but not as big as Real Madrid. Did you know that with the exception of Bayern, Real Madrid have a positive win/loss record against every team they've ever played against ?