If you wanna make different characters, but still keep the multitude of strategies, then consider messing with the core rules. Maybe the "working class monsters" are cheaper but worse, or maybe they require a salary every round/every few rounds.
You could also expand on the character themes you already have, move the ratmen and pig to a beastmaster type guy, and the succubus to a cultist summoner type guy, so everything at the very least feels thematically different. (I would also personally love if the kobold grabed all of their siblings to make a faction)