Maybe I misread? My takeaway was that their frontend web server handled concurrency just fine and was happy to dispatch requests to the backend in parallel, but

Maybe I misread? My takeaway was that their frontend web server handled concurrency just fine and was happy to dispatch requests to the backend in parallel, but the backend couldn't keep up and the frontend returned timeouts. That's exactly what you get if you put a bunch of multithreaded web servers in front of a single-writer SQL database that needs to be hit on every request. Yes, most such cases should be rearchitected to not go through a single choke point. But my claim is that this isn't automatic merely by developing for the web, and going through a CP database system is a pretty standard choice for good reason.