I am not sure about the weapon thing,
The idea that you shouldn;t give the weapon back to the attacker, while valid is kinda misplaced here since it is not a real situation and besides throwing the weapon down is giving it back to the attacker.
This is where reishiki comes into play. Reishiki includes (among other things) the protocol from withdrawing at the conclusion of the kata, and also for exchanging weapons when you change roles. I doubt there's a ryu out there in which reishiki includes throwing down the weapon.