I'm sorry, but where do you get the 5-6 year number from? You couldn't get a game published if it took that long to develop and you'd run out of money long before you could even sell it to anyone. In the real world it takes anywhere from 24-36 months to develop a "AAA" title "from the ground up." There are developers who frequent this forum like razor1 who could lay it all out.
I could say more but I will just say it takes a lot to develop a game from the ground up and to say it only takes 24-36 months for an AAA is disingenuous at best. Especially for a large space sim.
PS: Not including SC own reality....