Incorrect. Again, Final Fantasy XI did not have any instances. Assault and MMM were more examples of them being clever and trying to hide this. (Pseudo-instancing)
For all intents and purposes, the exact same thing as an instance. The variations are so slight that it's pointless to try and categorize them by different names. The idea remains the same.
Guildleves isn't instancing. That's more akin to phasing.
I disagree. Guildleves are not phasing. Phasing changes elements of gameplay between players who have or have not completed certain objectives.
Example: During a quest you destroy a bridge to thwart angry beastmen from storming across and pillaging your village. From that point on, any time you visit the area where the bridge once existed, all you see now is splintered wood. Players who have not completed that quest or objective would still see the original bridge.
Another good example would be a rescue quest for an NPC. You are tasked with saving some poor ******* trapped in an orc hut. When you leave the village you got the quest from he is not present, but after completion of the quest the NPC is visible, possibly with dialog thanking you for saving him and an offer to sell you some item that wasn't available before.
Leves don't qualify because the affected area is only affected during the objective timer. It is possible that I have not come across the specific leve you are talking about, but I haven't completed any of them that have made some impact on my ability to interact with the world. Even if there are some, only those are examples of phasing.