There are differences between factions, “class” types, tiers and even individuals. There’s a good amount of information regarding thralls and their combat abilities in the Wiki, inked HERE. It lists only T4 ones, so the “hidden” multipliers etc. may vary on lower tiers. But the basic idea is, each thrall has a separate bonus for melee and ranged damage, and they don’t always correspond to their classes - there are some archers with a higher melee than ranged damage bonus, but the difference seems to be pretty minor, usually.