Seeing as I don't believe Solas to be Dirthamen and thereby not Dumat - I think I'm good. Even if Dirthamen were Dumat, which I doubt (the likelyhood of it being Mythal is simply too high given the birth date of Andraste and the Children of Andraste Codex entry) it still doesn't affect Solas.
These two ideas are connected, actually. This is only theory of course, but Mythal can only take on a physical form if the being is a willing host. Once Dumat was freed, Solas-as-Falon'Din entered the dreams of the mortal woman Andraste and convinced her to do so. She accepted, at which point Andraste-Mythal and Solas-Shartan tore into the Tevinter Imperium until the sheer mass of the slave rebellion meant social Chaos was a more direct threat to Balance than Order.
At this point, Solas-as-Falon'Din enters Maforath's dreams, twisting and compelling him into betraying Mythal-Andraste at the precise point when Tevinter is willing to grant the largest concessions, the most land, that would still be stable and governable by rebellion forces.
So much blood, so much death and betrayal. But all for the greater good, yes?
For balance, because balance preserves Choice. And Choice is the only thing that matters.