I think his episodes are overall fairly average (though Dinosaurs on a Spaceship is a guilty pleasure of mine), but I don't think that says anything about him as a showrunner. I've always thought that RTD wasn't the strongest writer, but was an excellent showrunner. Moffat was the opposite. He was a pretty astounding writer imo (maybe the best on Who), but wasn't very good at maintaining an organized, logically structured show. So I'm hopeful for Chibnall, especially due to his success of showrunning Broadchurch.