I prefer to use ghouls over fiends myself but they are absolute trash in every aspect.
While I agree with you Basilisk on the above post, I do not believe giving hp is the way to go because the Ghoul unlike other 2 food units is a lumber harvester first and attacking unit second. This fact is the real problem, they can not buff the ghoul too much since it needs to maintain its cheap cost as a resource gatherer otherwise it throws off undead’s early economy composition if they up the cost. Giving the ghoul +2 armor and +20 hp makes them almost a footman that can gather wood, that is pretty broken, and you would need to up the cost significantly like around 20 gold or more.
I don’t know how to improve the ghoul that doesn’t screw up things unfortunately, maybe instead of adding hp or speed to them they could be left alone and decrease their gold cost to 100 or 110. This would make them more easily massed allowing more dps on the field, the only side effect is quicker lumber harvested in early game but I mean if you are going ghouls your not using lumber anyways.