Was it not Balthazar who betrayed Ketheric by striking a deal to summon
No that wasn't Balthazar. There was the head of the Guild (sorry, forgot the name) in the town that striked a deal with Raphael to get the Sharrans killed. And Raphael sent Yugir. But he also betrayed Yugir because there is one Sharran/Dark Justiciar in the gauntlet that escaped him because he himself stroke a deal with Raphael and turned in all these rats. So Yugir could not kill him (the last Sharran) and therefore was trapped in the gauntlet.