IMO I think comparing it to most lenses is kinda ridiculous. It's like trying to compare a Ford with a Bugatti Veyron; they are designed with two exceedingly different goals, and made to do entirely different things.
In the case of this lens, it was designed to be as near optical perfection as possible, with no compromise in any other part of the design. Both canon and Nikon could do the same thing, and probably do it very close to, if not on an equal footing. But when they make a lens, they have to make it to balance out optical quality, with size, weight, cost, and all the bells and whistles we come to expect.
Having said that, this is still a beast of a lens that will find its home to people who value optical quality over all else. But for the rest of the world, it's a lot like that Veyron, or the Concord; an experiment in what can be done, that most of us will have to look at from the sidelines.