The code guidelines in their benchmarks represent real programming practices in those languages. They promote "idiomatic" code because it is meant to represent the typical quality of code in the real world. Obviously many of the examples could be made more performant, but in doing so you would made the code less representative of the real world. Example: the typescript code outputs wanky ES6 features that are slower than their old plain js counterparts (classes, arrow functions, let, etc). You could abuse the ts code until its output is identical to js, but you would have a pointless benchmark now.
What would the benchmark honestly represent if the code looked nothing like code in the real world? The theoretical speed of the language just doesn't matter.
In fact, JS engines have been optimizing their performance around numerical benchmarks for decades. The benchmark problems (nbody, etc) are actually highly unrepresentative of real javascript performance because real world javascript is touching strings and awful DOM apis and messing with dictionaries all day.
Your 'real-world workload' should be stuff like text editor operations, a domain where JS's alleged 6x slowdown compared to C has not been remotely approached by current editors.