I would say, based on the number of posts, more people are using JS, jRuby, and Blocky now than are using Rules DSL, if that’s what you are asking.
With OH 5 we’ll get native Python 3 support too which I expect to become pretty popular as well.
As for complexty, I have a several hundred lines rule in JS posted to the marketplace (Threshold Alert and Open Reminder [4.0.0.0;4.9.9.9]) for an example. Now a little more than half the code is error checking and reporting. Typically your average complex role will be much shorter. (Don’t skip the marketplace though, why code a complex role yourself when you can install a template like an add-on?)
Based on my experience, any of the other languages are far better suited to complex rules with support for real functions and classes, libraries including third party libraries (e.g npm, ruby gems, pypy), and they come with a helper library that make interaction with OH as simple and straightforward as it is in Rules DSL.