Quinn and Jeph covered 98% of the screams, when Bert wasn't having the crowd do the rest. Bert has either decided to stop screaming as much, or he just can't do it anymore, period.
the nasty ass screaming you hear is Jeph.
I pretty much stopped following the band after the first couple albums but as far as I've heard he completely blew out his vocal chords recording the first album and then touring on it constantly. He doesn't scream live or on albums anymore. He literally can't.