[fiiv]

> when people start making mistakes and bugs arise that infact hinders performance

That statement is true of any language stack.

> The reason Javascript is used in frontend let's use it for backend (even using the same programmer) seems flawed

I am a backend dev at my company and we use Node.js, and I can tell you while the frontenders are not great at knowing the APIs of the internal Node.js modules, for example, but can provide great PR reviews of the code in general, for overall logic, flow and readability.

As for your statements regarding in general, I think you'll find quite a bit of people in various orgs who do not know a ton about the intimate details of threading but are for example backenders using RoR, and they just install a server like Puma or Unicorn to abstract away a lot of that complexity.