I'm a bit surprised and amused by this statement. Firstly trading competitions prove nothing. They are normally a very small sample - very short periods of time. They don't give you statistically significant results.
Secondly languages aren't profitable. The trading systems they run are what make profits. Most systems can be run on any language. The reason you use one language over another will depend on which of these factors is important to you: ease of learning or coding, robustness, availability of libraries, speed, support, ... and so on.
Arguably C is the most profitable language, or perhaps assembler / machine code ,since you can't run an HFT system on anything slower, and HFT is the most profitable method of trading. But anything slower can easily be run on python, java, R, ... you name it, as long as its turing complete.
Python, java, R, C++, Matlab are probably the main languages that people use (not in any particular order). Each are good for different purposes.
Now I wouldn't personally use R to run an automated trading system. I have in the past, running a portfolio with a few hundred million. But I wouldn't do it again.
It's absolutely fine for developing a system, ie. backtesting. It's pretty popular amongst the AI, DL, ML community, probably equal with python:
https://opensource.com/article/16/11/python-vs-r-machine-learning-data-analysis
But the type conversion, error handling and memory handling make it insufficiently robust for looking after my money. You can write robust R code, but it's much harder than writing robust python. The way it does objects is ugly as well, but that is personal taste.
GAT