Actually, I think what it makes you a competitive developer it's to dominate very well a programming language.
For example, if you are a company that needs a development team for the company website (supposing it's a very complex website 😂) what would you contract?: A Pro in PHP or one that knows php, but he is not a pro,but he also programs in JavaScript but he isn't a pro, and he knows HTML and CSS but he isn't a pro. Well I don't know you but I would contract the Pro in PHP.
Hope was useful!! Good luck!