My thinking goes: understanding classic OOP is helpful in learning JavaScript because the high level concepts are the same but in my opinion more obvious and easier to implement in Java/C#.

By more obvious, a Java/C# (+ others) program starts with a class and to add functionality you either have to add more methods to that class or implement another class. So to a new programmer "duh, everything is an object and objects are instances of a class".

It's kind of hard to convey the same idea to someone in JavaScript when {} is called an object, "xxx" is an object, and to compose a new class, you compose a new function.

However, to someone who already understands classes and objects, it's just a new/different way to create classes and objects.