The one language to rule them all reasoning is a red herring. We chose nodejs for our server code for an iOS app as do many others.<p>The reason why JS + node is popular is becasue it&#x27;s pretty good at each of the metrics you mentioned. Even though it&#x27;s not best in class at any one of those, it is well balanced for many tasks. Many other technologies are either too slow, too low level, too hard to scale, or too cumbersome to work with.