A whole cut is not any harder than any other shoe...maybe less so. In fact, it is the style I teach students with. But because it is such a blank canvas every aspect must be approached with a somewhat higher degree of accuracy and finesse.
Many many whole cuts I see posted on SF look to me as if the maker didn't have a clue as to what to do with...how to handle...the stitching at the bottom of the facings. Such awkwardness gets lost or covered when a shoe is pieced but it stands stark on a full cut.
One line of stitching...worse, two...around the topline is going to draw the eye because there's nothing else to look at. If it "wobbles" it's going to be seen. The eye is going to be drawn to that deviation...even if the conscious mind doesn't register it, the subconscious mind will. And it's going to detract from the shoe.
That's the challenge of a whole cut.