the only real "use" of the 2hand class weapons that can be used with a shield is the ranged defense a shield offers, they are iirc 35% or 30% slower in this mode(that goes for "mace" "morningstar" bastard sword/longsword/katana)
their are several 1h class weapons that can be used with a shield or without one in 1h(or 2h mode as the secondary) and they do not suffer the slowness(IIRC also damage penalty) that the few 2h class weapons that can be used with a shield in 1hand mode *langes messer is one for example*