We have different opinions, it happens. In my opinion, if you want to be a JS developer in 2019 you MUST know ES6+ features, expecially if you’re working with libraries and frameworks such as Angular or React. React alone isn’t “standard JavaScript” as it uses JSX, what do we do? We don’t use it because it’s not the standard way to write JS code? What about Angular decorators? What about Angular templates? To me, things like destructuring, spread operator, arrow functions, default parameters and template literals (just to name a few) are a must know, if you say they’re unreadable it’s just because you (or your team) don’t know or use them, I guarantee. If your code is unreadable is not because of ES6, maybe it’s the opposite :)
Also, if you think you can stop your learning process because you’ve been doing it for 20+ years, I’m sorry, that’s not the way to be a developer. It can be true for other languages, but the nature of JavaScript and browsers in general requires continuous learning.