For example, a UI / UX professional being asked to appraise a website screenshot may determine that the image in question has "desirable" traits which are inherently not deterministically measurable. Such as, if the interface elements have strong information hierarchy, or if they are deemed to be "fashionable" with current UI trends.
...but that's an example of a UX/usability matter that can be assessed objectively and non-subjectively.
Is 16 px or 14 px a better font-size value for a subheading, in a hypothetical layout? Immediately that kind of decision, where both options are objectively good for 12 px paragraph text, suddenly becomes an issue of taste that cannot be evaluated crudely by an algorithm.
But, if you have a proper well documented design system and you tell the LLM to use the DS and to avoid styling hacks they can generally do it. Even the dumber ones than Sol 5.6.
Of course only if the design is achievable in the design system.