Gardner, like Heisey, plays mostly LF, can also play CF, and hits RH pitchers better than LH pitchers.
Their career splits against said righties:
Gardner steals more. Heisey has more power. Both play good defense. Gardner is a year-plus older.
So, basically, by swapping out Heisey for Gardner, you'd be giving up Cueto, a year of prime age, and 147 OPS points.