What you're missing is that it's basically a Ruined Village on the turn played. Hence my suggestion of +1 Card.
right, but you already get a phantom card the following turn.
Flagship: I play Flagship, I target a smithy. Now I have 6 cards in hand. Next turn the Flagship comes into play and I start with 8 cards, and 1 action left.
Scheme: I play Scheme, then I play Smithy. Now I have 7 cards in hand. I scheme the smithy. Next turn I play the Smithy. Now i have 7 cards in hand, and 0 actions left.
So it's still like scheme with a phantom action, except it's -1 card in the turn you play it, and +1 card in the following turn. That shouldn't really make it much worse though.
It does have the disadvantage of being a duration card, and therefore you need two instead of one for the effect. You could also argue that it's a worse variant of scheme, which may be true. But worse =/= weaker.