So let me get this straight:
Let's suppose you flop this objective along with the swamp one. You fetch a spider. How exactly is DS ever playing more than one unit now? You swoop in with the Falcon, deal its damage, and focus whatever tries to get some damage on this objective, and repeat. Now the game is balanced enough to 'award' the opponent with more edge-cards so they can strike first and end the nightmare, making this 'lock' far from all-powerful obviously, but it just seriously cuts down the fun-factor, especially considering this set's main and Yoda their abilities circumvent the restriction. I also shouldn't mention that the Yoda you get will snow under the DS unit with focus tokens. Playing both the Yoda-event and the main (upon playing their big unit) makes for a nasty attack on your next turn.