@LysandersTreason : the city quests are the ones where they would get a better understanding of the adventurers personality, which is something that they need if the higher ranks start interacting with more important individuals (nobles), and setting the requirement a rank or 2 before that would give them time to try and correct the adventurer's flaws.
It is counter productive to just give the rank to someone who causes problems for the guild, or lets their rank go to their head.
Though I would expect most meet the city quest requirement well before the other requirements for C-rank.
Though it really depends on the nature of the world, but if they want the adventurers to not be social outcasts pushed to the fringes, then a system like this makes sense. If it is all about combat, then you get the series where adventurers exist on the fringes of society, and are not fully trusted.