Must just be your area. Where I live we have roundabouts all around (I have to go through 3 of them to get to my closest hardware store) and I don’t really see that many people that have issues with them. Worst we have to deal with are cars who are too slow to get into the roundabout and wait forever, or drive slowly and clog up the roundabout, but those are pretty rare thankfully.
So just swap new drives in one at a time, after backing your data up just in case. I upgraded mine to 4x10 drives 3-4 years ago, and its painless as long as you wait for the resilvering process to complete.