Once you reach scale, Ruby can be a limiting factor depending on how much latency impacts your revenue. And it's not so easy to remove that dependency as I've seen.
Usually what happens at scale is that the SQL database starts slowing down as more data is loaded in. Partitioning, indexes and painful refactorings aren’t prioritized. Engineering will champion “a faster language”—that incidentally allows them a new data model where they add in proper indexes at the start. They aren’t really incentivized to realize they could see the same gains by just improving their existing data inside the Rails monolith.
Source: experience improving performance (including latency) with multi-billion-dollar Rails monoliths
We should all be so lucky