> like 90% of the tests are catching things that would be caught automatically if we had used a proper language with strong types/compiler

It sounds like the tests are testing the wrong thing

> seems optimized for shoving crappy REST endpoints out the door as quickly as possible

Ruby is a general purpose language. Perhaps it is Rails that you have gripes with?

I'd also like to hear what you are doing that leads you to the conclusion that 'ruby is slow'. For most domains I would say ruby is fast enough to solve the problem in a way that customers are perfectly happy with.