I think he's knowledgeable about a previous world (and the Fade). Just not this one. He barely likes this one.
Something happened to the entire world order.. I know not what.. Yavana hints at it in the comics. And I think it's this world Solas prefers. The world with no veil.
And he can screw off for all I care. It must've changed for a good reason. Because it's closer to our real world now. And I like our real world.
What Solas wants is the equivalent of ME3 Synthesis. Except with spirits and demons.
I'm not sure if it was that different, there was always a separation between the Fade (dream world) and reality, otherwise a few things don't make much sense: the Crossroad, the Foci+Anchor, etc. The difference is probably how thick the Veil was and probably how people interacted with spirits (didn't saw them as tool, but person).
Thedas is full of people believing that "the grass was greener back in those days" too and that doesn't help. Storytellers deform everything to make them look cooler than they are..,
Anyway, I love bringing Cassandra to the Arbor Wild, she's really annoyed by "all that nonsense" (I got a lots of disapproval there, but she still loves me). Cassandra is probably the only character who is going to digest everything we learn in DAI. Not sure exactly what will result of it though.
Also, am I the only person who came to the conclusion that we need at least 3 "Creators" running around? Fen'Harel, Mythal and who murdered Mythal (I didn't find anything about June in the Mythal Temple, but I could have missed it).