I believe that I've read that elsewhere. They allow for better and higher flow than an intersection, but have a weird failure mode at very high rates where the circle gets loaded and all directions thus stop.
It's rather that if there's a continuous inflow of traffic that usually doesn't take one of the exits, then all traffic coming coming from that exit doesn't get a chance to join the roundabout.
What usually happens is the roundabout gets traffic lights.
