Depends what we mean by fast. I have seen Erlang VM handle 100k requests per second on a distributed cluster. That's plenty fast. Moreover, because of fault tolerance, it means ability to have a better uptime, with less people on-call. "Fast" can also be measured to include that, if system goes 200k requests per second, but crashes at midnight and stays down for a few hours, the average "speed" can be quite low. In a laptop demo that's not visible, but in practice that's money and customers lost.

But if fast means, "let's multiple some matrices", then yeah can probably use Rust or C for that. It all depends on the problem domain.