Well, not exactly a battle. The question isn't which one the best ovedrive pedal is. Because these two pedals are totally different beasts. The King Tone Duellist is based on a Marshall Bluesbreaker and Ibanez Tubescreamer (much like the Analogman King of Tone) and the Cornerstone Gladio does glorious Dumble sounds. So that wouldn't be a fair comparison because it comes down to taste and needs.
We wanted to see how these two compare. And how well they work together. And man, do these two pedals create some sonic MAYHEM together! So, yes. You want both of them.
King Tone Duellist
Two Rock Studio Signature combo
Universal Audio OX