Sometimes. If your profile is "lumpy" enough that can be true, but often the performance problems of slow languages manifest as annoyingly flat death-by-a-thousand-cuts profiles. (Especially after the low hanging fruit has been picked.)
Grinding another 5x out of a flat profile can be hard work requiring more creativity and producing less readable code than a (fairly mechanical) translation. Luckily these tasks also tend to crop up when design has stabilised and team sizes are increasing, meaning it can often coincide with the benefits of static typing becoming greater.
It's not a panacea, and it's
obviously both risky and costly. Shrugs.
(I've also seen the other case, FWIW. Wrote some C extension code called from a Rails app, and it was the right call at the time and we got great mileage out of it.)
Grinding another 5x out of a flat profile can be hard work requiring more creativity and producing less readable code than a (fairly mechanical) translation. Luckily these tasks also tend to crop up when design has stabilised and team sizes are increasing, meaning it can often coincide with the benefits of static typing becoming greater.
It's not a panacea, and it's obviously both risky and costly. Shrugs.
(I've also seen the other case, FWIW. Wrote some C extension code called from a Rails app, and it was the right call at the time and we got great mileage out of it.)