Getting hugged to death by a tree is bad enough, but he lost control of Egwene (who he was inflicting painful headaches on - not exactly as effective or useful as what Rahvin did to Morgase) and then was driven off in a rather humiliating fashion during the Cleansing (Callandor magnified Eben's fading connection to saidin, and hence the strength of Daigian's attacks - that is the only thing that makes this defeat understandable).

In my humble opinion, he falls beneath Moghedien in terms of overall lethality, so it makes sense that Aginor would attempt to use him to secure greater power with the idea to dispose of him once his utility had run out in "The Eye of the World" and that his only successful mission so far has been to free Moghedien from her collar.

Come to think of it, he nearly was captured by the Rebel Aes Sedai, barely staying a step ahead of them. Character thoughts aside, there is no way he could resist the traditional Aes Sedai Shield used against male channelers. With Egwene leading such a Circle, they wouldn't need the full thirteen to accomplish this, and there are more than enough Sisters in the camp who were capable of defeating him if necessary.