You've probably already Mastered React, I bet you've mastered CSS grid and Flexbox too, and oh you know enough of VueJS and Angular to get by.
I bet you're proud of yourself.
This is real life, bro.
In real life, people don't update their browsers, and others still use Opera Mini and, you guessed it, CSS grid will not work.
This is real life, and you will be forced to use Jquery over React.
This is real life, and in real life, You can't just dump your database tables and start afresh. Well, you can, but I cannot guarantee what will happen after you do.
This is real life, even if your internal APIs are RESTful, I bet you will have to work with some external SOAP APIs, tough luck.
I bet you hate to look at one thousand-line functions, I do too. I bet, also that you are itching to refactor. But can you, really? I mean, this is real life and so many other things depend on this one function, something could break you know. But hey, have a crack at it if you would.
We all love to build new products instead of debugging some old code written by some guy you never knew, who returns plain HTML from an API endpoint. But this is the real world, and you have to maintain that cash cow.
In the end, it's not about the languages you know, it's not about how much "ninjutsu" you can do with this shiny new framework. In the end, it's the basics that count.