Having been playing with a RL friend since Early Access, I have come to the conclussion that ESO makes it hard for groups.
This is especially noticeable with all the phasing, which more or less bugs something everytime for one of us, meaning quest npc's not following one person, or conversations ending too soon, so the other can't watch them, placing items somewhere can bug it for the other person and so forth.
Problems with group leader not showing, members going offline, while being online, aggro system is weird, can run past mobs and they all run to my friend instead of aggroing me etc.
I would really love to see the gameplay improve on the grouping side of things, because it really do become frustrating, to a point where you'd rather want to solo in the game.