Something that I noticed about Dain

I was re-reading Fourth Wing recently, and I noticed something interesting about what Dain says in Chapter 4. According to him, he can channel a significant amount of magic through his dragon, Cath, though at the beginning of Fourth Wing, he admits he's not very adept at it yet. This made me curious—has he ever struggled with his power? Or could his power be something more than what we’ve been told?

In Iron Flame, the only instance I can remember of Dain getting any development with his power is when Varrish told him to search for a specific word. But that’s barely any development compared to what we’ve seen with other characters