There are some properly large companies like github and shopify that run a large rails stack, it seems to work out pretty well for them. At my current workplace we have some streaming servers pushing about 15 gigabyte/second at peak load and the ruby processes easily saturate the available bandwidth on the EC2 instances. Like you say, the slowness of Ruby is greatly exaggerated. Sure we could rewrite the whole thing in Go/C++/Rust/etc, but it would not work any better and the gain of using 10% CPU instead of 20 is not really relevant since it's the NIC that is the bottleneck.