I think you definitely need to approach a 100k line project differently to smaller code (for example declare types more often, static type at least your interfaces and methods, etc) - but it is completely possible to write Groovy in a style that scales to that size and is still maintainable. After all, it can look almost exactly like Java.

On the other hand, it's impossible to scale Java down to the point where it would be sensible choice for what would otherwise be a bash script.

Even a 1k line project is unmaintainable when written in Apache Groovy.