I don't think the upright position, if that is what we are talking about, is uncomfortable, it is stock on most bikes the world over, not to mention motorcycles. I don't think it would be a comfortable position from which to make horsepower, but then there is a non-athletic form of cycling. The form where you wear you best suit to church, and arrive looking fine, just pop the metal pant clips into your pocket.
It is interesting that we have succesfully developed a high output method of cycling really fast, but it is that method that is uncomfortable and requires all kinds of specialized equipment clothes, and ointments to keep it going. Done properly it can be comfortable, or at least a lot of fun.
I tend to think of cycling as a slightly slower version of a car. It can be effective also as a slightly faster version of walking.
Cool 1x1 blog.