I think the 1 handed free ability could be something along the lines of what your thinking. I really don't think they need another re position. So many other class abilities grant those.
My take on it is based on the type of combat styles that single handed weapon users tend towards which is control in combat and not sheer power.
[Disarm] - 1AP, 4 turn cooldown -> deal 25% damage and reduce opponents AP by 2 for 1 round and reduce any weapon dmg by 100% for 1 round.
It has the same feeling as unique to having a one handed weapon without being the same as some existing abilities like re-position etc. Added benefits are no additional animations needed since it just a strike that has riders. I not quite sure if the reducing weapon based dmg is possible from the design of the game but it would be very cool and thematic.
