This issue is adressed in the known issues topic.
(Specifically the May 29 update).
The Gang’s All Here is supposed to give three new copies of the card; “new” here is means to imply that they are fresh, no bugs. But the animation incorrectly shows buffed copied added to the deck.
As to the AI - I don’t know whether it is intentionally weak, or sometimes just makes bad choices due to the complexity. I do know that on heroic mode the enemies tend to make much better plays (though I’ve also seen misplays there).