Can you elaborate on this? I've been upgrading it as heavy since the very beginning and this is the first time the damage values have gone down. It might make sense if the base damage were to drop and the scaling increase... but both are decreasing.

Because it's Heavy. Remove the ashes of war and try again see what it says.

That or a bug but I think it's the Heavy.

See the Guard Boost going up... that's also cuz of the Heavy I believe. Could be wrong tho.

Why will upgrading my hammer reduce the damage?