You noticed that too! But it was if Barry was lobotomized and now only cared about children, music,and wind chimes.
He seemed quite intelligently thoughtful and diplomatic in his televised Hannity interview -- neither coming down hard on his brother Barry nor overtly enthusiastic about his policies.
As for Mark's personality, he had the opportunity actually to have lived with tbeir father for some time, and observed him in his later stages of alcohol abuse, during which he beat Mark's mother. So no wonder Mark has a more realistic and objective view of their father than the "Dreams of My Father" fantasies. And he went into a mentally self-healing role as a musician. Good for him.