There are more beginners then there are experts, so in the absence of research a beginner UI is a safer bet.

If you're in the business of creating high quality UX, and you're building a UI without even the most basic research--understanding your target user--you've already failed.

And yes, if you definite "beginner" to be someone with expert training and experience, then yes an expert UI would be better for that "beginner". What a strange way to define "beginner" though.

If I'm building a product that's targeting software developers, a "beginner" has a very different definition than if I'm targeting grade school children, and the UX considerations will be vastly different.

This is, like, first principles of product development stuff, here.