This is almost a three year late reply, but I disagree with so much of what you said that I just had to write this.
I honestly don't understand how anyone could get the impression that Chuck or Blair or anyone got character assassinated for Dan/Blair of all people, a couple who had the most amazing buildup this side of Pacey/Joey but ultimately only got to be a prop for bringing back the tired toxic relationships.
Blair's character assassination in season 3 has nothing to do with Dan or a future Dan/Blair hookup. If it did, we'd have seen way more seeds strewn before 4.11. And if you really think all of Chuck/Blair's problems were sabotage for a ship that didn't even end up together and sacrificed for Chuck/Blair, I don't know what to say. Savage was still Executive Producer and she was writing for the show in season 3, so again, I don't know how you are going there with the writer insert with Safran. What I think happened was the writers had no idea what to do with Chuck when he wasn't being an a-hole that you love to hate (in the first half of season 1), a-hole that you kind of root for because of his heart was growing two sizes out of his love for Blair (season 1 second half) and sort of a tragic richboy Hamlet (season 2). So they write him as this weird 18 going on 40 businessman with mind numbingly boring business problems. Thing was, Blair was in a relationship with him, so her character is entwined with his. And since they didn't commit fully to her other story lines (like her being an outcast at college but instead of it resulting in any sort of character development where she realises she's been living in a bubble and progressing, they give her an out where she gets to go back to her juvenile high-school hierarchy drama with a transfer to Columbia), she has to be part of Chuck's boring story lines and she spends the entire season giving and giving and giving. Blair in their relationship was most of the times an accessory to Chuck's drama rather than both of them growing together.
Then the whole fiasco with the hotel happened which should have been the death knell for that relationship, but then he also sleeps with Jenny. Chucks manipulation of Blair to sleep with Jack in exchange for his hotel isn't exactly out of character for him if you realise he's a two time attempted rapist and that he also once compared Blair to a beast of burden.
And then the writers had the audacity to give Chuck a way out, instead of him suffering and grovelling at Blair's feet. He got shot, rescued by Fleur Delacour, lived in Paris as Henry Prince, got to come back to New York and date Fleur etc etc. Once again, Blair is the one who goes out to convince him to come back, she's the one who's giving, again and again. How much more onesided could this relationship get?
The reason people raved about Dan/Blair was that it was a breathe of fresh air compared to all that came before it. They were fun, drama free, heartfelt and something we hadn't seen till then in the show. The biggest reason was that Blair finally wasn't the only one giving, they were of value to each other. She was finally getting some positive reinforcement. Hell, first half of season 5, Dan is the one who's always giving, standing by her side when she doesn't even know if she's having the Prince or Chuck's child. Compared to the toxicity of her and Chuck (which got even more toxic when Chuck almost punches her in a drunken rage), whatever little problems they had (like the salon episode) were small fish.
Blair/Serena friendship had already reached a point where it seemed like they were only friends because they were friends since they were children. Them feuding over Columbia was the straw that broke the camels back for me. I'm not really sure Dan/Blair did much damage to them.
Season 6 is an abomination and the worst half season of a television show to ever exist. A hack job. Dan as Gossip Girl is stupid beyond belief and the whole thing should just be ignored because it makes everything else that came before into a huge joke. If it's canon that Dan is gossip girl, it is also canon that he reacts with shock to gossip girl posts when no one is around, sends out posts that ruin his own relationships and then angsts over it, made himself a social pariah through his own posts etc etc.
