@Gwyvian, I like your theory! It's funny you mention King Arthur, as I was watching the Mists of Avalon the other night, and I was thinking something similar....about the Inquisitor. But I could see Solas having accomplished something like that in his day. Explains why both sides felt betrayed when he....did whatever it was he did, and his confusion over who his "people" are if he had one foot in one tribe/faction, and the other in a new one at court. I wonder if this is what he considers to be the mistake? When you split your loyalties like that sometimes one side ends up getting hurt, or both.
As for the political theory, in light of the JOH codex on the Forgotten Ones, I think you might be right. It does sound like they were having an argument about "divine right of kings" or something similar with the whole "deeds" vs "nature" thing. I don't know if the political pararells are intentional, DAI is the most spiritual themed of the series so far, but I see it. The only problem there is Morrigan at the well, when she speculates that the gods were just ancient rulers (and thus long dead and powerless). Solas implies she's wrong. Clearly the Creators weren't just regular elves masquerading as gods, but they really ~were~ more powerful and had abilities others didn't, if not being actual gods. Which begs the question about what makes a "god" in the first place.
Thank you! 
Well, it's only natural to think of the Inquisitor as this type of hero, since the purpose of such a fantasy is exactly that a hero embarks on a quest - and as is true of games, you play that hero instead of just following their story, as is true with other genre fiction media, so spot on. Regarding Solas in his time, I think there's definitely something to be said for the dangers of playing for both teams, it would make sense that the only possible outcome would be... dramatic, to say the least.
As to the spiritual and political themes of DA: I agree, it's primarily more spiritual, but I'm convinced that this is merely the surface - this could be considered as literally the politics of the spiritual world, there is plenty of mysticism, yet more than enough room for "real world anchors" as I like to call them. Things that you can relate to in your everyday existence that helps you translate the spiritual content into mundane realities, making the mundane extraordinary and the spiritual content less overawing and more palpable.
Morrigan is a good point - I'd say that this is another case in point that the spiritual and political implications are actually inextricably intertwined. It is clear that the pantheon do have powers beyond the comprehension of "mere mortals" like Morrigan, yet I think Morrigan wasn't wrong when considering them rulers; the difference being that the actual hierarchy did not even remotely resemble the rules of modern Thedas, i.e. they actually had things to back up their claims of godhood, and the people chose to accept that. Also, we don't know much about the people who they ruled, I have to point out, comparatively a commoner of Arlathan could have been considered almost godlike in modern Thedas, so that means that the ruler of such a person, let alone a god, would have to be that much more impressive, and to this again I'd point out the pharaohs - it is not an unheard of concept to elevate equals to a godlike status because of their rulership, and this being a fantasy game, why not make that happen in a more literal sense and actually give them powers that sets them apart? The human myths were generated based on firm beliefs that tend to be reinforced by a whole host of things, so for the people of that time, these things were self-evident and true to most, if not all. To the elves, it could have been that from the pantheon's perspective, they knew they were different, if not gods, and they exploited that fact to elevate themselves above all other elves.