R's great strength is finding the interesting bits of the data. Testing the Algo. Doing the R&D basically. Better than Python.
Once that's done, why stop at Python? If your game is production, Python will do it, but others will do it so much better, faster, more efficiently.
Unfortunately I can't go into specific details without potentially divulging proprietary information, but broadly most of the issues I've seen in production with R are corner cases involving multithreading with large amounts of allocated RAM (over 100GB), and corner cases involving the data.table package. I've also seen packages that update and break backwards compatibility, although that's less of an issue. The biggest concern we have with R, however, is that the documentation and coding practices for most R packages make small bug fixes difficult without having extensive knowledge of the package code. This is not always true, but it's true enough of the time that we can't afford to maintain much production R code.