Disclaimer: I'm not Ruby programmer. I evaluated it once, saw no particular reason to use it instead of Python and promptly forgot about it.

With that said, the specific criticism(s) are:

• Poor performance. Sure. Ruby does appear to be somewhat slower than Python, but I'm more concerned about the peak memory consumption which is admittedly frequently pretty terrifying. Mind you, if I need high performance, I'm not likely to be using either Ruby or Python. It's fine for automation scripts, rapid prototyping or experimentation, hypothesis validation, moderate data processing, analysis and visualization, but yes: If you build your (supposedly) hyper-scalable website on Rails or use it for the system software for your embedded device, you're going to have a bad time. Every tool has its place (except Brainfuck). Don't use a hammer when you should be using a screwdriver.

• The above also covers the railing against rails, about which I have no further comment as I've never used it. Maybe it's nice, but if you're working on something with more concurrent users than your homelab automation UX, there's undoubtedly better alternatives.

...And that appears to be it. So it boiled to down to "performance". Does that in and of itself make Ruby "not a serious programming language". Well, if it does, then the same applies to Python. Does it mean that there's probably a better alternative for any given application? Probably yes.