Maybe, but requiring both skills to be "great" and "awesome" in order to be anything more than "passable" is a little unfair, no? Are there situations for which "passable" is indeed doing a good job?
And yes, it often takes longer to code features than it does to draw and place their UI elements.
My point was that most good coders can implement a designer's UI a lot faster than the UI designers.
For almost all situations I think you are better off getting two developers with complementing skills rather than two jack-of-all-trades that can do "everything". If you can only afford one person then seriously consider how to contract out some tricky parts of the weaker skills to an expert. Then you have a good foundation to build on.
And yes, it often takes longer to code features than it does to draw and place their UI elements.