They're always a drag on the show. It's shaping up to look like Ross, Jeselnik, Schumer, Gottfried, and/or MacFarland are the regulars now.
Surely there are other comics talented enough to roast these people?
David Cross
Patton Oswalt
Jim Norton
Doug Stanhope
Marc Maron
Come on, let's see some more comics.
Carrie Fisher's set seemed very awkward. She still had some funny jokes, it just seemed like more work for her.
The celebrities must not watch roasts because they always seem so surprised when they're attacked. I think they just need to hire writers for the celebrities so that they're better prepared. I enjoy seeing celebrities at the roasts, but you're right, they aren't as funny as the comedians.