The thing with R that I think is important to note is that you don't have interactivity to support code (eg in ruby and python the huge advantage of the repl is to interact with the code you are writing while you're writing it) but rather your code is a way to the make interactive experience better. R is an amazingly advanced calculator.

The reason I use R over python most of the time is because, despite some amazing improvements in this area by the python community, there's no better tool for fluidly interacting with data that offers the same power.

That said, R is not for writing software systems. People used to refer to many interpreted languages as "scripting languages", and while this is clearly not the case for Python and Ruby, this is exactly what R is. There's a good reason in RStudio it says "New File > R Script". The limit of using R is when you have a bunch of scripts that interact with each other to create a bunch of visualizations/reports. If your system gets more complicated then that, write it in something else.

Of the many language/environment combos I've used, I don't think I've found one better for rapid prototyping than R, and following from that R has no place near anything that would be called "production". I also happen to think, if used properly, this is a good thing since it means your "prototype" never accidentally creeps into suddenly being your production system.