Ruby is slow, but it is however faster than Python last I checked, with like for like code.
Python gives you other interesting ways of going fast (a lot of high performance plugins for numerics, Cython, and so on), while Ruby is a higher level more expressive language IMO, so you have more ways to shoot yourself in the foot more powerfully.
AFAIK with the latest JIT in some contexts pure Ruby can be faster than using C libraries, just because the VM can be better optimized and there is no overhead in moving data between the two realms.
I don't recall exactly where I read it, but I think was a while ago when they announced one of the newest JIT engines.
I recall something similar statement and I think it was from the YJIT team, they suggested that more and more people write pure Ruby rather than using C extensions because the YJIT compiler cannot see C code, it's like a black box to it, so it cannot optimize it further. Which means that in practical examples, YJIT has been able to optimize pure Ruby code to the extent that it in some cases not only beat the C extension but also surpassed it
More Ruby code means more room for optimizations that the team can identify and add to the compiler
Python gives you other interesting ways of going fast (a lot of high performance plugins for numerics, Cython, and so on), while Ruby is a higher level more expressive language IMO, so you have more ways to shoot yourself in the foot more powerfully.