well you must be sick and tired of me by now but you haven't complained so ill keep at it .
My first impressions with the young umberdroth are that its tactical regeneration ability is op for a unit ready from the very beginning.
My reason to think this is, mites mob and bandits are not really strong opponents but in the beginning of the game i only have my sov, my champion and slave explorers(if i am playing magnar) but normally just my sov and my champ, i can take out these enemies with my sov and champ and not getting any of them beaten but normally both of them end pretty banged up after a fight or two so i have to stop and recover.
With the young umberdroth i could go beating mob after mob of starter enemies with little to no damage to my sov and champ and the umberdroth recovering fully or almost fully while taking out these start game enemies with a lot of ease and even taking banished ogres(who are a little trickier) very easily.
so yeah i would advice to remove regen from the first umberdroth or replacing tough(+3 hp level) with endurance(+1 hp level).
edit: got an elder umberdroth noticed they are no longer in warrior temple tier but a bit lower, their stats and price seem balanced enough except for the very one thing i said before, tried them in several battles vs altar faction and they had similar tier units(boar spears, warhammers shortbows and the like) and again i found that the regeneration ability gives them that extra edge that makes them stronger than they should be i think.
I mean the AI managed to hurt them on several occasions but they recover and in the end outlast every other trained unit of the same tier.