It is true to a large extent.
This season Athletic Bilbao are one of the only teams to really take the game to Barcelona and they very nearly got a shock win. Last night Milan ignored the aura of Barca, and contested well, although there was a distinct gap in quality.
But I have to disagree with you on Mourinho, at least since he got to Real Madrid.
When at Chelsea and Inter he faced Barcelona with an arrogance, urging his players to contest and not fear Barcelona. And he gained much success in doing so.
Last season at Real Madrid he had better individuals, and went to the Camp Nou with the same attitude and they were outclassed, 5-0. For the rest of the season he was terrified of Barcelona, adopting the most negative tactics ever seen at the Bernebeau just so that they might scrape a draw. He was certainly fearful and intimidated by Barcelona.
This season things might be about to change though. They were a bit unlucky in the season opener against Barcelona at the Camp Nou, but they will be far braver in the first league Classico.