I could be wrong but I just think something that big is too hard for consoles and would probably create horrible lag..... Lol why can't anyone fix their NAT type......?

Eso and planet side are that big. There are ways to design around that, but a dedicated server is required. You couldn't host in on a p2p network which is what destiny uses. What it comes down to is there is no persistent world that you can load into a meet up with players outside of your fireteam, whether it is instance based or one giant world. Even if I could run/fly from the earth to every other plant if I can't load into a specific zone and meet with people it's not an open world it's just a spliced together closed (meaning hosted) instance zone.

Yeah but also there is so little content that in a dedicated server where bosses would respawn after 4 minutes farming would destroy the game.

Bosses can still be instances. The only thing a dedicated server would do is put everyone on bungies network with a larger number of people on the same server allowing for persistent worlds. The persistent world is just the starting point, most MMOs then break of that persistent world into smaller instances. Currently bungie just skips the persistent world removing the need for deviated severs and breaks everyone into small instances. This is why I said it may [b]SEEM[/b] like a MMO but it isn't. They could've designed it to be an MMO easily, but that doesn't take into account all the rebalancing they need to do in order to make the open world playable. I'm not saying destiny should or shouldn't be an MMO, I'm just saying its close to being one, but it isn't one. I think it could've been an awesome open world MMO, but I agree they defiantly would've had a much harder time making this work (I think they took the easy way out).