I love R more than any other language I have ever used. Perhaps more than any piece of software I've ever used. All of these points are valid, and yes, it's messy, and if you try to write the same type of code that you would in Python, it will frustrate you. And yet.. it somehow works. It makes data analysis and statistical modelling a pleasure. It somehow gives off a sense of lightness, and makes it easy to investig…
The main issue I've had is speed. As soon as you have problems that can't be vectorized, models that take 30 hours to run in R take 30 minutes in python.
This seems highly unlikely, based on my 20+ years with R. Yes, using wrong data structures/algorithms can lead to slow code, but switching languages won't fix this.
rprof and microbenchmark are your friends if you really need to optimize your code.
and (as in python, and as several others have pointed out), if you have something especially challenging, write it in C/C++/fortran instead, and link it to R.