I guess it is a bug and not intended that all Relic Hunter Slavetakers which as well are fighters, have all the same amount of Hitpoints, doesnt matter which tier they are (I, II, III).
I think here the I - III is more like a name, and they’re nearly all the same.
But isn’t obvious, and not like usually thralls are named. But all are in fact fighters III in theyr relic-hunter class. Would be nicer give them a name.