If the the Twitter fail whale is your concern, then your perception is outdated. Twitter started moving off Ruby in 2009. Both the CRuby VM and Rails have seen extensive development during that decade and a half.

I never worked at Twitter, but based on the timeline it seems very likely they were running on the old Ruby 1.8.x line, which was a pure AST interpreter. The VM is now a bytecode interpreter that has been optimized over the intervening years. The GC is considerably more robust. There's a very fast JIT compiler included. Many libraries have been optimized and bugs squashed.

If your concern is Rails, please note that also has seen ongoing development and is more performant, more robust, and I'd say better architected. I'm not even sure it was thread-safe when Twitter was running on it.

You don't have to like Ruby or Rails, but you're really working off old data. I'm sure there's a breaking point in there somewhere, but I very much doubt most apps will hit in before going bust.