Having read the rules again, on P54, it says independent characters need to roll separately to activate force weapons, so I guess it would only be sensible that it works the other way round again, so you are right, no S6 force weapons.
But you can still get S6 PW for the Paladins with Draigo's attacks still force weapon attacks, and at S7 at that! Best of both worlds, and better than S5 Paladins (S6 Draigo) with force weapons all round unless you are fighting a whole squad of T4+ multi-wound models.