It makes sense that Felassan was Solas' agent or even a slave(tattoos!) and was killed for failure. Makes sense: Fen'harel references, fear of the Fade in the end. However, while Dread Wolf is a pretty anti-hero figure, with all those tales and tricks and lies and intrigues, it does seem more than a little cruel. Especially if you remember Solas being such a bleeding heart in DAI, helping the refugees left and right.
So, I was confused. Could Solas/Fen'harel kill Felassan? Did it suit the character? And then I started thinking. Being a rationalist means being confused by false facts rather than by truth. That means, if you really don't understand something, there's a good chance you're looking at the facts the wrong way.
Who has slaves with tattoos? Who needs eluvians really badly? Who is absolutely aware of what's going to happen, and knows the gist of Fen'harel's plans? And who would kill or sacrifice their agents for failure without a second thought?
(raises hand) Fleeeeemythal, is that you?
Seriously, that _would_ make some sense, except probably not: all the clues still point to Fen'harel killing Felassan and Felassan serving Fen'Harel, including "she reminds me of you", it's probably him, and it breaks my heart I think we need a talk with Solas in that DLC.
(though then again, Imshael calls Felassan "slow arrow" and calls all others "mortals", so he could be something more than just an ancient somniari. Well, spoilers for the next DLC, I suppose!)
Briala is being a ******, though - I really felt for killing all the dalish and that noble mage girl.