Monopolies are never good for industries, just look at Pro Wrestling in America.
Sega would have been better off if Sony hadnt made the Playstation, it caused them to rush a lot of things and then Bernie Stolar came from being in charge of the American Playstation to being in charge of Sega America and he made it not have 2D games or RPGs, then ultimately killed the Saturn. Sega would have been a strong number 2 to Nintendo after the the N64 would have been a 3D cd based console since the Saturn wasnt originally going to be a 3D machine. In fact the N64 may not have been a 64 bit system, and the Dreamcast may not have been a 128 bit system. Microsoft would have entered the console market because then it would have been only Nintendo and Sega against each other. Sony would have only have made the cd attachment and hardware for Nintendo, it wouldnt have been an equal joint venture. It all rested on Sony not wanting to be a major player in the video game world, they did, so we got the Playtstation and here we are now.