WebGL focus good for three.js?

Would focusing and getting better at core WebGL make you better when you start using Three.js?

Also getting good at vertex and fragment shaders be useful too?

A proper understanding of the underlying native graphics API (like WebGL) is always beneficial if you are developing with a 3D engine. However it is not necessarily required, especially for simple use cases.

Advanced WebGL knowledge is definitely required if you want to develop more complex applications. For example without knowing shader development, it will be hard to develop custom materials with three.js.

Yes very true.

If we want to get better and make unique experiences then yes… diving deeper into WebGL core and shaders is extremely essential!