Having run a platform on RoR that did billions of requests per day, it scales just fine. It’s not as cost effective as Go, Java, Rust, etc., but it’s perfectly scaleable.
Scaling web apps horizontally invariably becomes more about where your data lives, how it gets scaled out, how it’s accessed, how work get processed (jobs), what caching you do, what memory requirements you have.... yada yada. Rails wasn’t ideal, but rarely are you ever working in a pristine “ideal” tech stack once you’ve hit scale and you’re 5 years into a business.
I think both statements depend on the definition of "at scale". I am no expert, but every RoR thing I have ever seen has been tiny in terms of traffic and still performed terribly. Is there anything in the top 100 sites using RoR?
There's quite a distance between "tiny" and "top 100 sites"! Some pretty darn popular sites that use Rails (afaik) are GitHub, Shopify, Hulu, Twitch, and Airbnb.
Not really. The web has become massively centralized with almost all traffic going to a small number of sites. The bottom of the top 100 list is only getting about 50 million pageviews a month, even poorly written sites in slow languages can easily do that on very cheap low end hardware. Pretty much anything not in the top 100 is dealing with a tiny amount of traffic, even a fair bit of the top 100 is. So it is github and twitch, neither of which actually do anything substantial in RoR any more. That seems like a pretty good reason to think RoR's strength isn't high traffic volumes.
This is wrong. GitHub is still a large Rails app. See presentations by the core Rails team people who work there like Eileen Uchitelle and Aaron Patterson.