If it's easy to scale your application servers horizontally, then language execution speed isn't very critical. Speed is critical for the things which are hard

If it's easy to scale your application servers horizontally, then language execution speed isn't very critical. Speed is critical for the things which are hard to scale (like your data store). And everyone is coming at this conversation like caching isn't a thing that you do on any high-traffic site (and lots of low-traffic ones too).