The chance someone who's never made a game and never even made a large piece of software of any kind could make a design document that was worth even a dime is about a trillion to one.
Game designers are the game industry equivalent of an IT analyst. What is an analyst? Analysts are there because programmers' time is too expensive to waste on details that can be taken care of by an analyst. Usually it's someone who has some tech skills but not good enough to be the alpha coder, or knowledgable enough to be sys admin, hopefully with some domain knowledge but the reason they exist is not because they are so awesome at anything, it's just there's a million details to take care of in making software and if you waste your only good coder on deciding all these details you won't be done for 100 years.
And so it comes down to you can't make software without programmers. It's like trying to make ice without water. You can't expect a random person to design software with good results, it will never happen. As soon as people see what they asked for they realize just how idiotic and useless it was, to the point they don't believe it's what they asked for unless you provide documentation to that effect, which is the long and short of why milestones exist. It's like a contract between the client or boss and the programmer, even when it's not part of a legal document.
And how does that help things? A lot if you have 20 programmers and a client who is suehappy. Not at all if you are making an indie game.
So even if you suspend disbelief and think somehow everyone on codex will fork over 10 bucks to make a game, and even if there's some way to ensure there's no theft of monies rendered, and even if you can all agree on who is best to run this, and even if you can all agree on what the perfect game is then it's still a giant waste of time. That is like a blueprint of how every piece of bad software ever made came into existence.
And without this money, how do you get people to do something they have no input in? Even from big name guy like brian mitsoda if I read about a "morale skill" in a design document I would start to think twice about working for him. The fact is as a hobby no one will every put out years of effort to complete a major game. As a business, it is hard to justify because anyone genuinely capable of doing this can already make a good living as a programmer anyway, far better than what even a 'pro' gamer will make. But if someone ever did do it they have all the power, because only they can make it happen.
And while not everyone is a great artist, you will become a good artist a lot faster than you'll become a good programmer. I'm sure there's an issue of talent involved in both, but I was surprised to find it easier to learn how to be an artist than I thought.
In fact I only learned in order to be good enough to know how things work for my own secret project, but it turned out to be relatively easy if somewhat time consuming. If you have gravitas, gird up your loins and really set down to work, you can learn everything about zbrush and maya in 6 months. Being an artist is more than that but books on anatomy and art are easy to come by. So are books on animation.
In fact as a programmer, it makes everything ten times easier. Sick of skinning? Make a plugin that does it in one click, like I did. Sick of how maya smooth works? Make your own smoothing for meshes like I did. You have the power to do whatever you want. For animation, it is ever more useful. It's just fucking joke to try to animate things today if you don't know how to program, you are at the mercy of someone who can make a rig for you to operate. But ultimately rigs suck anyway, if you are a programmer you can control things any way you want.
So, can one guy do everything to make a game? Well, I can. Not sure about anyone else. In fact I am 'done'. Well, not AOD done, since my software actually works and I have a game system that wasn't designed by a ten year old. not actually done, either, but all the software is working and now I am 'polishing'. By polishing of course, I mean making the actual game, its content, the art, etc. Probably I won't be done in a making monies sense for 5 years but I still feel pretty fucking smug.