Only a 7th but seems like a waste.

Idunno, makes some sense to me. The Lightning get something instead of nothing for a player who would otherwise become a UFA in two days. The Hawks get another veteran presence in a locker room full of young players, and it only costs them a 7th.

Why would Perry sign with a rebuilding team?

Probably for a chance to play with Bedard? Also maybe to be closer to home. Last I heard, his family home is in London, Ontario. If he goes to free agency, maybe he ends up way out on the west coast again.