Badly written R is impenetrable. So is badly written R. I suspect your standards for so-so R code are vastly different to mine.
R and Python really are very similar as languages. R is more functional, but that shouldn't impede your ability to understand code (once you master some of the basic idioms of FP)
I can't actually comment on what is good/bad R code, because I've never seen any R code beyond a few lines that I could follow.
The language matters. One is optimized for ... honestly I have no idea what R is optimized for. I don't think R works that way. It just is. Python though, its optimized for readability.