Archery is in no way nerfed at all.... its the most powerful thing in the damn game..... I had leliana or w/e her name is with 40 dexterity, use arrow of slaying and it did 460 damage.... by the way that can one shot anything not elite boss level (on normal).
I agree the arch demon should be a little harder... at least be harder to kill than that high dragon guarding the Urn of Sacred ashes that you can avoid...
On normal though everything is pretty much easy especially if you have 2 attack mages in the party (don't count Wynn as attack since shes a healer)
Thanks too cone of cold which is IMO the most usefull spell in the game followed by that entropy spell that puts all your enemies to sleep, then you can use Horror for 150+ damage, followed by that spell that makes all your enemies turn crazy and either stuns them or makes them attack eachother.
Without that mage crowd controll element idk fighting the arch demon on hard with no mage is damn near impossible.