A good designer has to have a fundamental understanding of construction and textiles in order to have their designs come to fruition. It isn't just about having a good eye. Simply put, you can't make velvet behave the same way as chiffon and chiffon won't tailor very well because it won't support all of the underpinnings (e.g., the interfacing, underlining, lining, padding, etc.) required to make a well tailored garment but velvet can can be tailored.
When I was in design school, students had to take several sewing classes and a textile class before they were even allowed to take their first design class.
And, I for one would not want to go into a building where the architect doesn't understand the basic principles of construction and engineering (and that is why they have to get a license to prove that they know what they are doing).