Tao edit: Lindstrom of <Companions>
A lot of those Tarhyl mobs are considered mini-bosses. Their strategies, difficulty, and loot are generally less epic than zone or wing bosses. Zone bosses tend to have huge loot tables like DoTo, Versikol, Thaz, Saitha, whereas the mini-bosses offer less loot for an easier kill. Every mini boss cannot possibly be harder than the previous zone boss. I would keep Tier 10-11 sanctum out of this presumption because I believe the difficulty scales up pretty evenly from Gongoerth to NZ and then Custodian. That is only within itself though, I don't know what I would compare sanctum to since content elsewhere around its tier was designed vastly different from it.
A lot of those Tarhyl mobs are considered mini-bosses. Their strategies, difficulty, and loot are generally less epic than zone or wing bosses. Zone bosses tend to have huge loot tables like DoTo, Versikol, Thaz, Saitha, whereas the mini-bosses offer less loot for an easier kill. Every mini boss cannot possibly be harder than the previous zone boss. I would keep Tier 10-11 sanctum out of this presumption because I believe the difficulty scales up pretty evenly from Gongoerth to NZ and then Custodian. That is only within itself though, I don't know what I would compare sanctum to since content elsewhere around its tier was designed vastly different from it.