"...with sufficient caching you can serve arbitrarily large numbers of requests with arbitrarily slow languages." Only if the dataset is small relative to the

"...with sufficient caching you can serve arbitrarily large numbers of requests with arbitrarily slow languages." Only if the dataset is small relative to the traffic rate, and if the data mutation rate is relatively small to the size of the dataset. There are plenty of systems that do not have these properties. I agree the speed of the language does not matter as much as people used to think... but the shape of the data matters a lot more than people think.