What's wrong with Solas as an antagonist? I think he has the potential to be a fantastic antagonist, with a really good story to back him up.
I can certainly understand not wanting to see more tragedy befall him and Lavellan. Goodness knows they've had enough crap for a lifetime. But as an antagonist, he's a clever, capable man with clearly defined strengths and flaws, and a personal relationship with the protagonist to boot. The last two BioWare antagonists who fit that bill were Jon Irenicus and Master Li, and IMO they were BioWare's best. They were more than "just" a good antagonist; their opposition to the hero informed the whole tone of the story in a more meaningful way than just stopping the bad guy from destroying the world.
And IMO it's pretty clear that while he's an antagonist, quizzy does not have to declare him an enemy. A quizzy who tries to redeem him still considers him a friend.
Solas being the true antagonist of Inquistion all along actually makes the game better in some ways.
One problem I had with the game is that Corypheus never felt all that particularly threatening after Haven, he constantly was being thwarted left, right and centre and combined with the rather lacklustre manner in which we managed to defeat him, he felt like a completely lame villain.
But by revealing that the man behind the curtain is really the guy we had been working alongside from the very beginning, who'd secretly orchestrated all the events of the game and used us to further his own goals, that is actually a brilliant bit of storytelling.
In many ways, Corypheus is like the Arishok in DA2, the villain we think is important, only to later realise that the actual antagonist of the game is someone else. Solas similarly borrows Anders role, as the trusted friend we fought alongside suddenly turned antagonist and revealing that he'd used us as an unwitting pawn to carry out his plans to change the world.
For people who hated DA2 and loved Inquisition, it's amusing that it's basically the exact same game when you get down to basics.