We don't really know until Incursions are out in the next update. As it stands right now there's really no need to even grind the missions. Most people I know are spending almost all of their time in the DZ to get to at least rank 50 to get access to the good stuff the vendors there sell. But the difference is pretty big imo, in Destiny you needed to grind a ton of shit just to upgrade your gear. It was mandatory. You can do whatever you like in The Division, really. And if like me you nolifed that game and are out of meaningful ways to progress already, well, can't really be mad at the game for that.
But yeah the seamlessness of the game world is really amazing to me. No loads to get into missions, nothing. The Dark Zone is just awesome too, there isn't really anything like that. But fundamentally, this is a loot game. I'm baffled there are still people who don't know that, or don't know what that is, or act like it's some kind of betrayal. "I finished the last story mission and only got a gun with better stats? WTF?!" I mean, what. Did you expect to be showered in endgame gear because you beat the story missions? It's just so weird. This genre has been around forever and still so many don't get it. It's okay if that's not for you.