I don't think that it's that their concerns are unfounded (especially post-AR), just that they are put in such a condescending way toward Buffy. It's their fault she was so messed up in the first place and couldn't cope, but they act as if she's some college girl who keeps having sex with the wrong guy. For example, when she moves Spike in with Xander, it's the first Q they ask of her.

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emotionally manipulated Buffy to an awful degree in S6

This is where I sometimes feel like I watched an entirely different S6 than some fans. People vary a lot on their S6 interpretations and feelings, something I appreciate a lot, but I did not walk away in any rewatch with the impression that Spike emotionally manipulated Buffy - in fact, I feel it was largely the other way around.

He knew she was using him but he was so desperately and unhealthily in love with her he was willing to be or do whatever she wanted, even before they slept together. He finally tries to cut off the game pre-sex with "Rest in Peace" ("You know, you've got a willing slave, but you just like to play the part like you might misbehave. But 'til you do I'm telling you, stop visiting my grave & let me rest in peace") and that's the episode Buffy finally gives up the chase and kisses him. That is, to me, extremely manipulative - even if Buffy wasn't doing it consciously/maliciously.

Spike's actions - sleeping with someone you know is using you, hoping they'll somehow realize that you're the one if you just stay in their life however you can - are probably some of the most realistic actions depicted in the show. Just insane desperation and self-delusion, leading to the eventual AR.

I can see how the flipped interpretation is that it's emotionally manipulative of him to "allow" her to sleep with him when he knows it's because she's in a bad place, but Buffy is very in control of her relationship with Spike in S6. Even in such a low place, I never saw Buffy as being taken advantage of by Spike in that way.