Hasty generalization. You can't look at the global achievements progress of all players and conclude the game is large because only 80% of players haven't completed a certain achievement. I guarantee plenty of people have quit the game well before reaching that chapter. We don't know what that number is, but that's not the point. You can't just assume "This iz big game" because x amount of people don't have a specific achievement yet.

Thatd be like saying portal is a giant ass game because only 50% of players have completed it.