True here. Groovy has truly pathological performance in some areas.

I wrote a web service that read and processed XML documents. They were large, but not enormous... Couple hundred kilobytes, usually. My first cut, using Groovy and its built in XML DSL, took up to 15 seconds to process a single document. Rewriting in Java/StAX, it was a couple hundred milliseconds.

From then on, my MO was to write my code in Groovy and then rewrite anything that got called more than a few times per request/run in Java. Groovy's fine for glue code, but its performance was a real barrier to regular use.

As for JRuby, I suspect it's because no matter how good JRuby is, it's a second-class citizen to "real" ruby in the Ruby ecosystem, and to built-for-the-JVM languages on the JVM side. It's a great product, but it does have a few impedance mismatches coming from either side.