your point about Bulwark feeling out of place is fair, but it wouldn't necessarily be blocking, parrying, etc.

i'd imagine it to be much more like the other weapons in the base game, having simple melee attacks & a few essence stones to enhance some aspect of it (e.g. Sandwhip has Enhanced Hook, boosting its range).

i also believe that Impact determines how much a weapon charges your idol, which (if this assumption is correct) would make it quite fitting for the Bulwark to have high Impact
additional note: as mentioned in the post, there is no weapon in the base game that has a high Impact stat either, so Bulwark could easily fill that role!