> Ruby has concurrency problems [...] standard libraries don't default to evented IO, and the GIL messes up threading, both of which can be footguns for anyone trying to build a resilient and scalable service.

Yes, but this article is about speed, not concurrency, because speed is a thing 3.0 didn't do a major improvement to from the last 2.x release.

There's no need for a “Why didn't Ruby 3 improve concurrency/parallelism” article, because it did.

Fiber#scheduler addresses your IO issue, and Ractors (while still experimental) are aimed at the parallelism issue.