Yeah, the Ruby VM certainly is slow, but that doesn't really matter for most realistic workloads. In Twitter's case it definitely made sense, but do keep in mind that besides switching to Ruby they also switched their entire architecture around to a paradigm that Ruby had no mature ecosystem for at the time.

Node.JS is much faster both because it has a fast VM, and because it has concurrency much better dealt with in its standard library than Ruby does (i.e. a proper event loop is built in and its use is idiomatic).

That's not what the original blog post was about though, it was about how bad Gunicorn is. I've written Python, but never web apps (since Ruby's superiority there is obvious), but I don't think it's really fair to judge the whole language based on the use of some popular library that's shitty. I think it's symptomatic of Python that the library is shitty, but that's my dislike of Python shining through. The reality is that there are most likely great Python libraries for dealing with concurrent web requests, and she didn't bother to learn them.

On Ruby the community would without hesitation recommend you to run Puma or Passenger or even Iodine or Falcon or whatever fancy stuff you have nowadays. These webservers all deal with concurrency, optimizing memory usage, load balancing and managing queues correctly. They don't have silly things like fork'ing before importing libraries, because good software architecture is something that's highly valued in the Ruby community.