Like I said it's my theory alone, with no proof whatsoever, the initial game scope is no longer the current scope, that's why you see discrepancy's in the stretch goals between what we have now and what was talked before.
Even if we choose to say CIG has been in development for 5 years
while ignoring the fact that they had no up and running studios and staff prior to 2014 you still have them doing 2 games at the same time, so to make it fair you cut the dev years in half and you have 2,5 years of development time for each portion of the game