This seems pretty nice!
It may be a bit weak, because usually, the other player can trash a copper or estate and not pick up anything. And mid-game, they might do things like trash a terminal action and gain a village or trash a village and get a card-drawer (if they have a hand of like torturer-torturer, maybe the can trash a torturer for a workers village, if they have a hand of like festival-festival-festival, maybe they can trash a festival and gain a smithy).
On the other hand, if they trash a copper, then they've cutpursed themselves, and it's not optional. If forcing them to trash a copper shuts them out of a gold or a powerful $5, that's pretty strong. And late-game, you might force them to trash a silver in a hand of like Gold-Silver-[good terminal action] - province-duchy.
It works well when stacked, too. If you play like four of these, you're not going to destroy their entire hand, you'll probably just force them to downgrade a bunch. Which is a big hit because expensive cards are hard to get, but it's not going to be a pin, they'll still have a hand, unless, like it's a four player game and EVERYONE can play like four of these each turn.
Like develop, its strength is going to depend on whether there is a smooth progression of costs; if there are good things at a variety of costs, then it's power to you is strengthened, but its attack part is weakened (since the opponent isn't forced into a gap).
It doesn't seem like a power $5 to me; I would think it might be okay at $4. I guess you'd have to playtest it to see for sure whether it's good at $4, or whether it needs to be $5 but have some sort of minor bonus like +1 or 2 cards or coin or something. I would suspect that as it is, it would be a bit weak of a 5-cost card.