While there is indeed a Ruby on Rails tax, Github is also written in Rails as well (https://github.blog/engineering/architecture-optimization/bu...)

So is Shopify and Stripe. They can scale.

These days, if I want something that has some of the ergonomics of Rails in a platform I know can scale better than Ruby, I reach for Elixir/Phoenix.

Github can get pretty sluggish as well; if you have a pull request with lots of comments page loads begin to take a dozen seconds or more. AI code review bots make it painful for humans to use it.