I would have to strongly disagree. The modern web design process requires intense collaboration between designers and front-end developers, so much so that it becomes a painstakingly long process to implement designs. Someone who can fulfill a designer +dev role would eliminate a lot of those wasted hours of back and forth. There is a also a ton of crossover in knowledge/skills between a designer and frontend dev. I would argue there is more of a crossover between a designer/frontend dev than someone who is expected to know both frontend and backend as a full stack developer. Regardless of whether you are a designer or developer you can always improve your skills so specializing in one area does not equate perfection. I designed and developed my companies latest marketing website entirely by myself. From concept to code and everything in between. The kind of quick iteration and creative freedom we had working with me as the designer and the dev would of never happened if we had to work with multiple developers who specialized in certain areas.