Solas may not have said everything he knew about the Blight or Archdemons, but I think he's pretty clear as to what bothers him about Wardens throughout the course of the game - he thinks they're simplistic and overzealous. Their duty is all that matters to them and they think their duty is to act, without stopping and thinking about consequences "like a fair lady that chases the butterfly off a cliff. (But if you don't stop them, we'll all fall)".
I've mentioned it at one point before and I'll do it again, but I think there's something Blackwall said that summarizes problem with Wardens well (Blackwall may not be Grey Warden per se, but he IS a Grey Warden fanboy after all) - I paraphrase here: "it would be better if people fought evil, instead of trying to understand where it comes from".
I don't think I have to say how problematic such statements are? Action is needed when necessary of course, but it's just SO easy to deem something as evil and work up oneself to fight against it, instead of trying to dissect the problem and deem it as more complex than it seems.
Wardens may have good intentions, but those good intentions will likely pave the road to hell - it possibly mirrors something Solas thinks he's done in the past, which probably adds to his freak out about the whole thing.
.... Or, he may have witnessed what happened if people went digging for Archdemons before - after all, there is a codex (http://dragonage.wik...d_Elven_Writing) in Temple Of Mythal that suggests that this may not be the first time someone had that idea.
As for Soals not offering any better solution - well, we don't really know what he knows and maybe he thinks that there's nothing people in modern Thedas can do in the long run.
He DID say this to Blackwall after all:
Solas: I will remember this. When it is over.
Blackwall: This? This war? The Inquisition?
Solas: The people. How you fought against the tide. It is... courageous.
He also admitted to Varric that, for all their flaws, the Wardens managed to buy some time for Thedas. So he obviously knows something, but apparently he thinks that aside from buying time, the best things Wardens can do is - ironically - not make things worse in their zeal to stop the Blight and Darkspawn.
In Solas' eyes, the situation with Wardens seems to be the "one step forward, two steps back" type - for all the good they can do while delaying the worst, they may as well possess enough power to bring catastrophe to Thedas much earlier than it's anticipated (by ancient elven entities and who knows what else).
This is one of his main flaws, IMO. I adore his character in many ways, but for everything he is eager to criticize, he offers no good alternative. Wardens, circles, the Dalish, all he does is deride them without offering ways for improvement. I bet his mistakes in the past have something to do with being too eager to bring down the establishment without thinking of something to replace the chaos that follows.
I don't really think that's the case. People don't want to listen to him, much less to (controversial) solutions he might have. He did say (to disliked Inquisitor) that he's grown weary of not being heeded and that in time it grinds away - so it may be that he just learned to not say much, as he thinks that people wouldn't consider his ideas anyway.
Also, don't forget his long banter with Sera - how he lectures her about what to do with Jennies, how she should eliminate forces that are acting only to cause chaos and replace them with those who will do the hard work of establishing new order. He's also baffled at her not thinking about the actions of her organization in the long run, or any sort of long-term goals and just seems to want to have fun.
Aside from that, through the entire length of the game, Solas establishes himself as someone who is all about thinking ahead and looking at a big picture. So I'd say he does have some ideas and solutions, but there's really not much he can share without giving away his 'ancient elfy'/'Dread Wolfy' status, because the keys to his solutions likely lie beyond understanding or acceptance of most people in modern Thedas.