Roundabouts with high traffic flow in one direction can lock out other low volume approaches. 4-ways enforce equitable access.

Yeah maybe for a few moments. So what? It's a low volume approach. Sometimes people gotta wait and sometimes waiting to let a massive traffic flow get through quickly is the better way to prevent larger traffic problems.

You've apparently never been stuck at a roundabout with non-stop commuter traffic streaming through.

We have roundabouts everywhere in the UK and that almost never happens.