Having carried him in my party all game and got through all of his party banter, and actually having done his romance from beginning to end, I absolutely disagree with all of that, and I do think that discreting
all of his character prior to the judgement as completely dishonest is unreasonable. There are parts of his arc where he is maintaining a facet, obviously, but there are many more where he shows his true character (romanced or not). Between his conversations and banter, you do know the real man behind both Blackwall and Rainier - you can even tell him that in judgement, that you free him to atone as the man he
is, not the man he
was or the one he was pretending to be.
In his romance, which is your specific criticism, in the very scene that activates the romance you can tell him against his own protests that you see good in him that even he doesn't see. That's not about the title he's carrying, but the deeds that show who he is. There's no headcanon involved in this - by the time of the judgement, you are not starting over from zero, you are choosing to work through this with the person you fell in love with, and not his title. If you can't see past that, you have the option to break up, but I don't think it's fair to essentially say that people who romance him and don't give up on him are romancing only his Grey Warden persona, instead of the real person he shows himself to be, regardless of name.
I don't blame you for being resentful of the character, but I do think it's quite unreasonable to be stuck on the notion that everything he says is a lie and not see past the lie to acknowlege all the things he does and says that are true and do reveal a true character beyond what name he calls himself. That's partly what Cullen's dialogue in that jail scene is there to say. If we are to live by that notion, then everything Morrigan, Anders and Solas say to you during their stories is a lie too, and we never saw a single moment of genuine character from any of them. Since their reveals only come at the end of their games and nothing else was done in terms of character development beyond that, did everyone who romance them romanced only their lies too? That's what I mean when I usually refer to double standards - if we are willing to admit that there were moments of those characters that were genuine, that were honest, that were themselves before their reveals, then disregarding all of Blackwall's character prior to his confession just comes accross as disingenuous. His character arc had the same premise as theirs, and I don't think you'll find a single Morrigan, Anders or Solas willing to say they never truly knew the character they were romancing before their lies came out to light. We acknowlege fault in certain characters but completely handwave others, so what gives? What is the standard?
In any case, we've agreed to disagree about this before, so... we carry on disagreeing.