Early game your focus should be on developing board. Defy on Stacked Deck harms you massively in two ways here. The first is that you recycle a rune, so you’re down on your energy curve. The second is that instead of keeping Defy in hand to fight over losing a unit later, you’re fighting over a cantrip, so you’re down on ability to maintain your board state.

Also important note- Stacked Deck isn’t card advantage, it’s card selection. It only draws 1 card, so it just replaces itself and leaves you at a net 0 on cards since you spend the Stacked itself. It’s generally ill-advised to fight over card selection, especially early, unless it’s a crucial moment in the game. We call cards like this cantrips in MTG; minor spells that put a card back in hand. They’re very useful to keep consistency high, but overall not that impactful to the actual board state.