I'm definitely of the mind that young Fen'Harel was more of a villain than he was a hero. He probably frittered around, messing with the pantheon and the forgotten ones as much as he could without being labeled an enemy of either. Or perhaps, both groups humored him so as to not unseat the balance of power. I don't think he had a lot of slaves. He was probably never that sort of god. But he certainly enjoyed the perks and freedom that came with the facade.
Then, something broke. Some god went too far, and Fen'Harel had the sobering look around Arlathan and realized he had become the 'good' one by merit of savage company. And once he started caring, it all snowballed out of control. Which would explain his somewhat chaotic attempts to fix things. It wasn't really the role he was ever prepared to assume.
Which is not to say he doesn't want to be the hero- I think by the time he's Solas, he has reformed most of his old ways. But he carries that guilt, along with the guilt of not being able to handle the situations handed to him properly. He's still trying to outrun the shadow that was cast over all of the pantheon, a shadow that probably hovers over him as well.