The source you cited was reliable about the Michael Graham and Chris Plante firings from WMAL in the past few years, so I have no reason to doubt this.
That station is going to lose market share. Who the heck is going to listen to amiable, inoffensive, namby-pamby Brian Niemann? They’ve tried other experiments, including the disastrous Bill Press, and nothing worked for them except fireball morning drivetime hosts. Conservatives like some meat in the morning.