"The 100 killing with canons is the same; only 1 toon needs to fight"

Not true. There are two boats and your toons will get split up, been there done that. It'll take at least two goes at it (one for each ship) but fortunately it's fast and easy.

Add to the list the PVP quest (only have to do 5 duels - counts for everyone). I just got two pairs of DK's dualing it out on auto-attack and repeated (goes faster once they're almost dead from the first fight) and then one more fight.