Jarl unit according to its description is supposed to do extra damage to myth units but doesnt have any multiplier on its unit card. so either description is incorrect and needs to be fixed or the unit card is missing some values
I believe jarls used to be a hero unit. Now godis have taken over their role. But the text seems to be new, so it migt be they forgot to add some bonus. When they were heroes, I think they did full bonus damage to myth units.
Jarls used to have some minor bonus into MUs, like a x1.5 or something. It’d make sense to at least retain that, give the Norse a ranged, cavalry, and infantry hero (of sorts).
The history information is leftover from the original when Jarls had bonus damage versus myth units and so needs to be updated. They’ve removed the bonus damage because they added a new Norse hero. The in-game description now says “Good against human soldiers.” Not sure why.