I don't see how that could possibly be true. The same flow has to be achieved either way, and lights will always have some margin of inefficiency in switching. Seems lights will always be strictly worse than roundabouts in this sense.
There are also solutions for large vehicles where the center is raised but not impassible.
You over estimate the intelligence of the average American. I've lived in a few cities with a number of roundabouts and while I love them, the number of stupid people that panic and..
-stop in the roundabout
-stop before the roundabout and let their brain buffer for 30 seconds.
-somehow go the wrong way in the roundabout
-fail to yield to traffic in the roundabout
Is way too damn high. It makes traversing one a high stress situation since you have no idea if grandpa grunt and run in to you is about to perform a confusion based terror attack on the traffic control device.
Texas for example must have too much lead in the water because people seem to chronically get them wrong.
Indiana drivers seem to much better in general with a lower incident rate of "omg that guy almost hit me".
With this said roundabouts that service a fixed area, such as a neighborhood without much cross traffic seem fine in general. Whereas roundabouts in areas that pick up new traffic are far more prone to incidents. And god help you if the roundabout is in a tourist area.
One of the problems with roundabouts in the US is there are too few of them so you're always running into someone who has never dealt with one before which increases the risk of unexpected behavior.
Anecdotes are meaningless. I’ve driven in Texas where there were roundabouts and it wasn’t ever a problem.
Don’t forget that at a roundabout the risk of injury from unexpected behavior by other drivers is _lower_ than at a signalized intersection. There’s a good reason why the injury rate goes down wherever they are built.
There are also solutions for large vehicles where the center is raised but not impassible.