Pick an ARCHITECTURE that make simple to do things in parallel.
People are saying that python and ruby can't do things in parallel in an easy way.
While technically true, it is also pretty much irrelevant, since we have multithreading.
I think it's relevant. Let's say you write an API that only needs to call another API that takes 1 second to respond. A golang or nodejs server would have no problem to serve thousands of parallel requests. You can't really justify having 5000 ruby threads, they are heavy and they will use too much memory.
If you prefer some other paradigm then Concurrent Ruby[1] has a swiss army knife of them including event loops and Go style SCP.
I think things will improve in ruby 3 but even without ractors it's still possible to do either async IO in MRI or use JRuby for fully parallel ruby.