How to articulate the difference between design principles and aesthetic style?

One of the barriers I've encountered within UI design is a blurred distinction between implementing proven design principles and a designer's judgment for aesthetics and style. I would like to know how to best articulate these different influences when discussing within a team, and with stakeholders? With the goal being, to improve one with minimal impact to the other.

To elaborate on this further, I'll give you an example.

A UI Designer creates a new comp. Technically it's sound, and there really are no usability concerns. The designer has even factored in proven design principles such as the Golden Ratio or Fitts Law. Everything is great, and we could move forward with making a good product, except... it could look better. The design team is attached and thinks it does look good. After all, it uses the Golden Ratio! So how could it not? The stakeholders are impressed, the developers are on board, so what is left to critique without nitpicking?

The Inverse Problem

A UI designer comes up with a slick, shiny, impressive visual UI design as a high-fidelity mock-up. This would be impressive on dribbble or any other established gallery. While they didn't use the Golden Ratio, they used their own judgment, and they're talented enough that it still looks amazing. The design even includes common, familiar, UI concepts. So stakeholders are impressed, and developers are excited to get started. Everyone is enamored by what they see. But now the problem is, it could work better.

To Recap

I think it is best to marry these separate influences as seamlessly as possible, to make one final amazing product. But in my experience teams tend to focus disproportionately on one over the other. Sometimes to the point of sacrificing valuable quality in one area of potential influence.

So how do you explain, and quantify, the differences internally to a team and to stakeholders so that both get the necessary consideration without bias?