But the inefficiencies you sometimes see today can’t even be explained with any bad choice of language. You can create more than fast enough programs with interpreted languages with garbage collection. But then of course you need to know at least a little bit about data structures and not doing dozens of REST calls anytime anyone taps the screen.

What if doing dozens of REST calls is effectively the product?

Could you explain? I’ve got a hard time imagining a user interested in the rest calls themselves.

I only partially agree, an interpreted language can act as a hinderance when doing optimisations, for various reasons.

But how we write the code also matters of course.

Furthermore, competency also costs money. I’m not saying this to be mean to people abusing REST calls.

Most code is so bad that "optimization" isnt the issue, at least in no sense that a language/runtime would help with.

It's just designed with O(N^3) architectures, "servers on servers" and "callbacks on callbacks", etc. because, seemingly, new features are made by very jnr developers -- who glue these idiot-proof frameworks together ---- trading needed-knowhow for polynomial behaviour.