I do agree that there's something happening behind the scenes that's influencing the Derplander and his friends. Although, I don't agree that what he's doing is born from of some righteous or noble cause. My idea is that they are being influenced (Possibly tempered) by the Dark Crystal, and are setting out to collect the elemental crystals to empower it, just as we did for our crystal. But as Hydaelyn wants to cast out all darkness, the Dark Crystal wishes to do the same to light. It isn't about balance, but rather exterminating the opposing force.

If he came to some sort of revelation as you suggested, I don't think he'd be relishing the conflict with another Warrior of Light like we saw in the story. He would do what was necessary to balance the contending forces, but as a former Warrior of Light himself I don't think he'd enjoy having to fight us. He's become cynical, and mocking. Getting a twisted enjoyment out of challenging us. Perhaps as a warrior of light he grew jealous of our accomplishments? Perhaps it was these feelings of resentment that the Dark Crystal called upon to twist their minds.

Whatever the cause, I do believe there is something far more malevolent at work.