Having just read that Breibart is dissing McMaster now that Bannon has shown up back there, it may be that Trump recognized something in McMaster that Bannon lacked.

"Breitbart article,  "H.R. McMaster Endorsed Book That Advocates Quran-Kissing Apology Ceremonies," claims that he threw his support behind a book advising U.S. military personnel to avoid desecrating the Quran, so as not to inflame religious tensions with Muslim populations in countries where American troops are deployed.
It also quotes a blurb for the book by McMaster, in which he writes that "terrorist organizations use a narrow and irreligious ideology to recruit undereducated and disenfranchised people to their cause."

Just considering McMaster's resume of two Bronze stars, a Silver Star, his history as an Armor Commander in the Battle of 73 Easting, his PhD where he questioned the military's role in Viet Nam under LBJ and McNamara, and the rest of his military history, Bannon is just a mouthy toad in comparison.