Sure it gets exiled after, but free is a deep discount and four mana for a large spell isnt anything to sneeze at either
Its also worth pointing out that Salvation Swan blanks on a substantially bigger fraction of the creature roster, to the point where I think its actually a problem for blink decks
The trick to making Empty the Pits good in a control deck is finding ways to draw cards or kill your opponents creatures without putting pressure on your own graveyard
Keen Sense For only one mana, [c]Keen Sense[/c] can draw you many cards over the course of a single game, but only if you can sneak the enchanted creature past your opponents defenses
(When a creature with exploit enters the battlefield, you may sacrifice a creature.) Whenever a creature you control exploits a non-Human creature, draw a card
4 - Mox Opal There are five Moxes included in the Power 9 (scroll down for the full list), and while the effect of adding a single mana may seem a little tame, its a powerful ramp in the early turns