[Chris2048]

Is Jython good though?

Last I used it is had issues keeping pace, i.e. demonstrable memory issue that took a long time to fix, lagged considerably behind python 2/3 versions.

It's also worth noting, that as an essentially transcompiled language, you need to have a good appreciation of Java machinery, in which case languages like Groovy provide good competition.

[vorg]

When talking about JVM languages suitable for building systems, Jython isn't generally mentioned for the reasons you give, nor is Apache Groovy. Those two are good for scripting, e.g. testing Java classes, build scripts, glue code. Besides Java, languages like Clojure, Scala, and Kotlin are usually considered as systems languages on the JVM.

[Chris2048]

True, but I believe Groovy and Jython compete for the same space, if not system-building.