You bring a good point up Adrien. Asking for only group content nor solo content isn't a solution. But having the possibility to alternatively do this quest in group (or the other way solo) would be a great asset to the game.
And of course adapt the story in each case. =)

And as for other mmorpgs, my problem wasn't about doing scenario quest solo... But about NPCs acting like if I was the only one trying something out there and then go fight / do something for him with many other players. I find it a bit sad because there is then less cohesion in my opinion.

And I just have to take my console if I want to be the only hero of a game.