I don't deny the utility of Rails for building a certain class of web site. But I think there is a difference between Rails and Ruby, and a difference between use of a technology and improvements to that technology.
I think a technology must continue to change and adapt to remain relevant. I see Shopify as the main driver of current improvements to Ruby (the core features of the most recent release, and the upcoming release, were mostly due to Shopify as I understand it). I don't see smaller companies doing these improvements and I think without them Ruby will (slowly, because it's used in some big places) fade away.
Smaller companies can be happy with Ruby as it is while enjoying the incremental improvements. They're hardly going to invest in hiring C-proficient engineers to bolster the language - it's simply good enough to start a business from and the performance metric is low priority.
They're in a different class to heavy hitters like Shopify and Github, who will gain a lot more from investing in gradual improvements to Ruby's runtime at the scale they operate at.
I'll contrast it with JavaScript, which has tried to assimilate every language pattern under the sun over the past decade and is intensely difficult to maintain a stable stack with, even if it's better now than it used to be.
A lot of ex-Hubbers went to Shopify. Additionally, a lot of upstream commits to Rails occurred from things pulled out of GitHub. GitHub has (had?) an entire team dedicated to Ruby and Rails and performance and optimizations/improvements
I think a technology must continue to change and adapt to remain relevant. I see Shopify as the main driver of current improvements to Ruby (the core features of the most recent release, and the upcoming release, were mostly due to Shopify as I understand it). I don't see smaller companies doing these improvements and I think without them Ruby will (slowly, because it's used in some big places) fade away.