Woz and Paul Allen were pretty visionary themselves. I think working at the same company after they've made it doesn't appeal to everyone and Allen actually got sick and left. Microsoft was well on it's way to being massive so I wouldn't chaulk it up to Bill Gates alone.
There is one guy who is more invested in it than the others right?
You should get someone to help, but I don't think it would be good to have two founders who have visions for the company. Their respective visions would eventually diverge and then conflict would arise.
You can't have two people trying to dominate. Unless both founders have perfectly matching visions, their joint command will be as bad as design by committee. Someone is bound to leave or become somewhat subordinate to the other. In the end one person will come out as the main visionary guy for a specific company.