That is nonsense. If you can run your code on 10 servers instead of 1k servers, that is an insane time and money saver that could make or break a company.
For most startups the difference between Rust and Ruby is not 10 servers vs 1000 but rather between using 0.1% of a CPU or 1% of a CPU. A single server running Rails will easily scale to hundreds of thousands of daily users. Most companies never get that many users in the first place, and those that do will have the funds to afford rewriting the hottest paths in a more performant language.
I certainly don't claim to be an expert, but I have a hunch that getting to the point where performance becomes a significant factor (in the success or failure of a product) isn't going to be about the choice of language. I also think you're vastly underestimating the performance that good architects can get out of ANY (primary) language through good system design. Good design vs bad design makes the biggest difference in my experience, at least from a technical standpoint. Probably just nonsense though as you say.
