>DHH has only written web software and knows nothing about serious software development.
I don't particularly like DHH either but web software is definitely serious. Shopify (which you seem to have confused with Spotify) runs on Rails. So does GitHub.
Those are both huge platforms handling a ton of traffic. If GitHub isn't "serious software" then what is?
Some thing with multiple "nines" in its uptime.
Years and years ago I wrote a PWA for my wife and I to sync lists (packing lists, groceries, TODOs etc) cross-device. It's been running in a docker container and only goes down when the server reboots for kernel upgrades. That's at least five 9s of reliability. It has 2 users.
Is that "Serious Software"?