The reason there isn't anyone in the minister rank is probably because it requires like level 30 wisdom and no pirates with level 30 wisdom 1) exist 2) want that rank.
I was the only pirate with level 30 agility, and the only pirate qualified to be the assassin rank, and since I was the one who created the whole Rogue tier, I was happy to take that title, even though I was told later that I had been past over for captain many times because they simply knew I would rather be an assassin. Seriously, any **** can become a captain of a ship, how else do you explain what's his face with "Captain ____ _____ of the Outlaw Star (pirate tag yay)", seriously, naming your ship after an anime should be against the rules, considering naming YOURSELF after an anime is against the rules.
Anyways, Assassin > Captain, lvl 30 agility is harder to get than the requirements for captain. Therefor, it's more rare, and commands more respect than such a cliche'd rank as the ol' "captain".
However, I do agree that "Minister" is a pretty stupid thing to have in graal, but then what else could you replace it with, it's a pretty specific definition.
I mean, a wisdom tier would be like, monk > cleric > priest > bishop > minister? I knew when I was in KJ for like a couple months way back I was special and I obtained the rank "Mitsukai" ("angel" in japanese) and was higher rank than the head priests who had been in the kingdom more or less forever simply by asking for it.
Replace minister with "Archangel" or something, it would sound cooler and make people try alot harder to get thier wisdom up to become that rank, although, it would be kind of ironic if a balor priest got that rank.