The language used for a server backend is far from a guarantee of efficiency and performance. It's very easy to write a D or Rust backend that doesn't optimize

The language used for a server backend is far from a guarantee of efficiency and performance. It's very easy to write a D or Rust backend that doesn't optimize queries and handles caching badly; you'll get just as terrible response times from those as you would on the "typical" slow websites that you refer to.