DasUberGuy
He's thrown down with Thanos in HtH combat, who has destroyed planets and survived black holes.
He was almost killed.
And he had The Avengers on his side.
If He doesn't have the Soul Suck, then I imagine you're totally negating the Soul Gem completely.
Outside of the Infinity Gem, Warlock is just what he was created to be;
The Perfect Human.
Superman is a...well, you get the idea.
Sure Adam can survive in space and fly as well as utilize his own soul to create energy blasts...(and I'm not even sure how well those attacks would work without the Soul Gem)
But he's no match for Clark's combined powers, experience, and sheer will power.