I think that the Theif could have more potential than it has already, yes, it is very good at the terms of getting loot but I think it could ignore defenses like cannons and gun towers etc. (I dont have much knowledge of all the defenses since I'm a new player) and could play an important role in achieving victory on enemy bases! Plus defenses that specialise in taking out stealth pirates such as the thief could be implemented too! For example the harpoon gun. Plus other pirates with the ability to stealth could be added making the defense that specialises in eliminating these pirates would have a better purpose!
You want to take a look at the Thief character She has a stealth ability, but you're going to have to send her to the Academy and get her trained.
Oh well boy am i stupid , i didnt realize she had this ability, to be honest i havent even unlocked her yet so i didnt know, but nonetheless maybe other pirates could be added with this ability and a defence? Anyways im gonna go slap myself.