Well, github, just to name one:). Also shopify, digital ocean, stripe. I also worked on a large ruby app that was faster than another large Java app. Keep is mind that all these platforms handle a great deal of requests at any given time, so we're not talking simple web apps.

In my experience bad software design, bad DB design and bad developers are the major cause for performance issues, you rarely get to that level of polish with your app that the difference between different languages really matters.

At micro-bench level PHP always beats ruby pr python, but most apps have performance issues without ever getting to that level.

My funnies experience was with a java team that where baffled why their app is slow. I told them it looks like they have a huge bottleneck on the DB, their answer: "Yeah but it's java, it should be fast"