My point is that for all the talk of how performance doesn’t matter and that we can scale ruby, the real heavy lifting is not handled by ruby.

It’s not a “problem”, but if you’re going to talk about large companies scaling something you need to understand that they’re likely scaling it in spite of limitations.

Largely, some systems don’t scale too well (latency on network accessible cache, throughput in persistence layers such as databases) so a lot of application layers will lean on those things heavily and they are exclusively written in relatively “faster” languages.