Actually, it's not "just a pinning test".
It's a pinning test on 3d6, which has an average roll OVER 10, and is triggered just by being targetted, even if they fail to wound. Further, every skyhammer annihilation force I've ever seen has 4 of these devastator squads(2 full squads combat squaded to 4 squads of 5). But at minimum against an incompetent opponent, it HAS to have 2 of them.
So in general, 4 units of their choice would have to take these tests on 3d6 every round that they're allowed to shoot. While I suppose it's possible that your opponent missed something in their rules and didn't run it properly, if they did, even with leadership 10, you should have failed more tests than you passed.
EDIT: Unless they're playing the OTHER skyhammer formation from the kauyon book or whatever. But that one is worthless so I have no idea why they'd do that. It requires you to take 3 extra tactical squads and a land speeder, and only gives you the ability to run and shoot on the turn they arrive, without fleet. Any time I hear skyhammer, I automatically think "Skyhammer Annihilation Force" because that's the GOOD skyhammer. If they took the garbagehammer, ignore everything I've said up to this point. No explanation of your victory would be necessary for that particular matchup.