[vnorilo]

Types are the means of "improving language performance" without turning into C. It's all about encoding invariants for the optimizer.

I doubt a competent JIT is ever slower than a competent interpreter, but it may not be that much faster or worth the workload.

It depends on the size of the primitives. An array language could be close to 1:1, while for a cpu-level instructions you will struggle to reach 1/6 of JITted perf.

[rurban]

You forget this is ruby, which will not have a competent JIT. They have such a bad JIT with enormous overhead that only very special cases will be faster, most cases are slower and will wait for locks or be racy.