To the article's point, many/most JavaScript projects are not optimised and better performance can be achieved with just JavaScript, and yes, JavaScript engines are becoming faster. However, no matter how much faster JavaScript can get, you can still always get faster with other system languages.
I work on high-performance stuff as a C++ engineer, currently working on an ultra fast JSON Schema validator. We are benchmarking against AJV (https://ajv.js.org), a project with a TON of VERY crazy optimisations to squeeze out as much performance as possible (REALLY well optimised compared to other JavaScript libraries), and we still get numbers like 200x faster than it with C++.