You need to remember, they're still working on the same timeline. It's just that now they've got the PC, PS4, and Xbox Betas all at the same time, rather than staggering them like they were before the Alpha announcement. They would still be working hard on the game during the original "Xbox Beta" dates. It's just now the lucky few will get to play it twice before the final game is released.
First off The Division is what I have been wanting since the debut at E3 2013. The games you mentioned are completely different. Hitman in my opinion will not be real competition. Uncharted 4 comes out 2 weeks after, and Dark Souls 3 isn't until April. So that March 8th release date is perfect. If they push it back again they will have some monster competition. So I'm just hoping that March release date is a hard date.