I highly doubt that you will reach the scaling limits of rails unless you have a massive product and even if you do Python would not be a good replacement.
But there are more things in the world than CRUD apps. I'm building tools to track hate on social media, and there's a lot of social media out there. Rails, or any RDBMS-centered architecture, won't cut it. And if you're not using Rails, then I think the case for using Ruby isn't very strong these days; Python has a bigger community and is much stronger in important niches, like ML. So we picked Python as our default language not because the Python runtime is vastly more efficient than the Ruby one, but because the ecosystem is a much better match for our needs.
I wish it were the other way, as honestly I like Ruby better as a language. But my personal tastes are ultimately a pretty small factor when I'm picking the tooling for a project.
Great for CRUD, yes, but plenty more than that. Soooooo many apps don’t need to wrestle with a huge amount of data or even a data warehouse or analytics or a data lake or any data science or anything requiring even a blazing fast query time on a super complex gnarly data model, and most of those would ship faster by using Rails, and be easier to maintain as well.
But the devs don’t tell management that……
If you wanted a website to handle traffic rails or even php would be a better. Both have a more mature ecosystem and both allow for rapid development.