No, you're completely dodging the issue by saying some library functions, not written in Ruby, are not slow, and then talking about development time, which has

No, you're completely dodging the issue by saying some library functions, not written in Ruby, are not slow, and then talking about development time, which has nothing to do with the slowness people are talking about. The last time I checked, we're talking about the speed of code written in Ruby, and in particular, the speed of code as it's typically written.