Unique units are not necessarily “Power units.” Nor should they be.
It depends on your roster of options. Celts have the weakest paladin in the game, so not a power unit, they do not have good CA nor arbalest, so FU woads is a power unit for them, and infact is a late game options. It’s just not a great one unlike berserk for example
They are not trash, but are not great either, and their upgrade is expensive, and most importantly, they are not “raiders”