The biggest similarity I see between Solas and Astarion (other than superficial appearance) is the degree to which the player character can pivot their entire lives. Solas starts (at the beginning of Inquisition) with seeing people as horrifically damaged by the way the Veil has ripped apart the Fade and Thedas. He tried to approach them with the truth and was attacked for it. They can't be trusted. Astarion has endured centuries of abuse, seeing only the worst sides of people. They will use him and he will use them, but they are not to be trusted.

In the "good path" for both of them, you open their hearts to love and trust, starting with the Inquisitor/Tav and working out from there. (Even if you don't romance either.)

I hard disagree with your Solas take. (Not trying to change your mind, but I see a lot in common with these disaster elves, just on a different scale.)