I consider his statement about Taven in the same way i consider Cassandra's statement that the Chantry would also want that forgotten history. They're both stating the truth, not really saying which one they prefer
Of course it's stating what they prefer. They don't put words in mouths of characters if they don't befit them. And Cassandra would totally be for the Chantry, seeing that - while she has many objections and criticism - she wholeheartedly believes that it should be given a chance and be reformed.
In the dialogues with him, picking the "What about our allies" options, he specifically states that Cassandra, Leliana and someone-i-cant-remember are... lesser? And it's fairly obvious that the gets all flustered when The Inquisitor compares him/herself to them
That's not what happens at all. He states that Cass disassociates holy from mundane and thinks them separate. And you can't have more evidence of that than in her friendship scene, when - in reaction to Inky claiming that perhaps there's no higher power - she pretty much exclaims "then how do we know how to do the right thing!?", as if we need Maker to make good decisions, or everything that's good emanates to the world from some sort of divine source and people are small and lost without it.
Her faith and the way she sees it influences her so much in fact that - while she has a grace of bouncing back rather quickly - sometimes makes her blind to better solution enough to make her miss it. For example: she disapproves of doing elvhen rituals in ToM, while she approves when it ends with sparing the lives of Sentinels and Abelas. Plus she's too plagued with doubt and questions. It's an observation Iron Bull makes too, when we ask him about who is fit to lead Inquisition in Haven.
With Leliana he claims that her faith is damaged and she sees everything as game of tactics - which is entirely true if you actually do her mission. She almost lost herself; an admission she makes if we manage to steer her away from turning into Marjolane.
This has hardly anything to do with them being 'lesser': what he states is that both women are brilliant, but have gripes and biases that don't let them see the full picture; a quality he thinks approved Inky has and is by no means limited to them, or limited to the People. The Evanuris after all were all great and powerful and First of the People, yet Solas deems most/all of them as petty and fickle. So being one of the People, no matter how ancient and mighty, means little to him; being a good, smart, open-minded, level-headed person, no matter of provenience (if we get to the balcony scene he basically says same things to every Inky of every race, background or gender) with an ability to see the full picture is what appears to be important for him.
Also - where does The Inquisitor compares himself to them? Solas responds well to being appreciated, same way Dorian or everyone else does, but I don't recall being 'all flustered' after Inky readily makes comparisons between them or something. Obviously at the end of Trespasser Inky is Solas counterpart, but it's sort of the other way around when it comes to appreciation and comparisons, at least in terms of roles they play.
I need to make this clear, Solas' plan would be, either way, monstrous. The only difference is that by going back in time it could be argued that he's not killing the present-days people, because effectively those people never even existed. Tearing down the Veil (which is probably his plan) would just mean killing everyone in the hope that everything will become as it was
If Solas is going to, say, wipe away memory of modern Thedas effectively these people won't exist as well. And then again I remid you that we don't know if turning back time - especially thousands of years of it - is a painless process that leaves no trace. Judging from Redcliffe that's not what happens. The Avvar Augur comments in JOH make it seem like the Fade and spirits were aware what happened.
Now... the fact that the plan is monstrous is recognized by Solas himself, so it's sort of a no-brainer to say that it is. He himself tells us hat it's absolutely awful, and that he will pay the price for it possibly for all eternity, but he feels like those are only options he has left to have any chance to restore either the People or conscious connection to the people. Question you should ask yourself is therefore just how bad things are in his perspective now - how badly the world was influenced by being separated form the Fade and if it effectively doesn't mean more suffering in the long run that makes Solas think that his plan is actually worth following though with.
And as i'm writing i just found a new reason to dislike Solas and at the same time find him fascinating. He seems despise the Elves of old who played God with the "People"'s life, and yet now he's doing the same thing with the lifes of those, it could be argued, he himself created.
I hope i made this clear, i'm not saying he is an uncomplicated character, i'm saying that if he died with all the others Evanuris the world would have been better off and, this is the sad part, effectively no one would have missed him. Just as Loghain he survived his friends and his family and, again, just as Loghain, he will not stop until someone stops him. He probably is even aware of this, seeing the way he treats The Inquisitor in Trespasser, but it doesn't excuse him nor make him better than what he is, to my eyes
Well that's sort of the thing, isn't it? He's the old hero, a champion of people, who now has a real chance of becoming a villain, yet there's still possibly a chance for redemption for him. He wavers, he is plagued with doubt and he's open enough to - so long as Inquisitor shows him a bit of empathy - reconnect with the world and people he was ready to condemn, even after thousands of years of solitude, creeping loneliness and events that left him pretty much broken.
The fact that he's alive till now and suffers to see the consequences of his actions is also an interesting point - he's the character not given the courtesy of dying and letting other people take care of problems stemming from his decisions. It's like an elaborate punishment for him. I think it's fascinating rather than a point against Solas. We don't have situations in real life when people are able to see the effects of their actions thousands of years into the future - and with the way things go, either IRL or in the way DA setting was crafted, it seems that things can spin wildly off course and could make us feel guilty of our own actions, even if at the time we did't think much about them or they were reasonable.
That's where Solas is - the guilt gnaws at him, and since he's still alive; since he's possibly one of the few people who sees what coming (he implies in the game that both he and the world are running out of time, and not in a sense that he himself is about to end it) and maybe the only person to do something about the Veil, he's put in a very particular and very messed up situation. Where will it yet lead him and how much influence we had/have over him as a friend or enemy or else we're yet to see.