Having used both NWN and Roll20 I can say I definitely prefer the GM mode for building levels and encounters. There are more free assets available, the game graphics are excellent, and the editor allows a huge amount of freedom for modding (assuming you're willing/able to put in the time).
You can play DnD 5e in Divnity right now. People want the actual game systems converted (which is understandable because that would be super neat) but its not necessary. You can roll the dice to cast a DnD 5e spell and have the GM apply dmg to your target (targets). You would still need to track spell uses and other factors on paper but that is what has to be done in apps like Roll20 anyways; so its not like Divinity is lacking in this area.
That said lots of things could be improved including fog of war, player limit, and a host of other minor quality of life changes. If Divinity 2 DLC/patches steadily improve on GM mode then I see no reason why it would not become the best VTT available.
