The game won't be like The Division in terms of Open World it will actually be better, there will be more places to go to, and more stuff to do.
The Division currently only has, the "Light Zone", "Dark Zone" and "Underground" although the underground isn't explorable in the same sense as the other two.
Destiny will have I believe 4 planets with areas similar in size the whole Division Map, with less explorable areas since you won't have streets etc.
The beta only gives access to a small percentage of what will be available when the game launches.