To be authentic means something is real, to be genuine. When something is copied the copy will never be authentic.
Being truly original today when making art is close to impossible because although an artist may create something thinking no one has done anything like they’re doing before there normally is something close to what they’ve made. The way artists are taught in school to look at other artists work for reference also discourages independent thought, so new artist will often have a hard time creating something new, instead they will take old work further, like how Christoph Niemann shows in his 2002 cover of the new Yorker, he created the same image of the first cover of the new Yorker but he portrayed it differently by making the image entirely of pixel squares then turned it into a completely new image making it an authentic Niemann piece.
I agree that a lot of the principles of good design are still relevant depending on what you want your outcome to be. But some principles like ‘Good design is thorough, down to the last detail’ are helpful when you’re creating to not become lazy in your work. Most of these principles are made for very minimalist work, and not everyone who creates wants that from there work, some artists want there work to be busy because that’s part of their distinct style. Although a lot of contemporary style is very minimalist you can see this with our technology most of the designs of apps are very minimal with their use of block colour there’s little use of outline or shading in their appearance.

The New Yorker Cover (May 27,2002) Niemann

Ten Principles for good Design, Dieter Rams