Picard as written is so off base from all the backstory of the man we've received to date (with the exception of Dillard's Resistance which is just too silly on too many fronts to take seriously) that I find it impossible to believe in the reality of the character presented.
By contrast, the Picard we see in First Contact is wholly understandable. He's filled with supressed and pent-up horror and fear and hatred towards the Borg and the whole Ahab revenge thing works perfectly BUT he also retains enough of the compassionate man we have been shown him to be for over 10 years to know that he's still capable of listening to reason and to act on it (even though it would have made more sense to have had the lecture delivered by Dr Crusher, IMO).
In the Destiny trilogy, what we get is someone who presents as textbook clinically bipolar. He lurches from manic highs to the depth of total despair. I don't care whether this guy is your squeeze or not, if this is what you see as CMO you relieve him of duty and drug him up to the eyeballs while you're at it - even more so if you think he's being possessed or controlled or malignly influenced in some way by the Borg. I mean, the captain Mack gives us is crazy mad.
I don't think that's fair, because it ignores all that took place between those events, as well as the differences between the stories. In
Destiny, he'd just gone through a ten-month span in which he faced three separate Borg incidents even before the big invasion; every time he thought he'd defeated them, they came back, over and over. He finally admitted his love for Beverly, and then the Borg came back. He defeated them twice more, and once he thought he was safe, he married Beverly and was about to propose starting a family, and then he learned a group of drones had survived and posed a renewed threat. And then when he defeated them and was finally emotionally ready to start a family, Beverly had been pregnant for only a few weeks when the Borg began an all-out invasion. By the time
Destiny begins, the Borg had been attacking the Federation for six weeks, their biggest assault ever. And it just got worse from there.
So this is what's fundamentally different from the Picard of FC. He's a married man and an expectant father now. And it took him a long time to get to that point emotionally. So it's not just about the Borg side of the equation. Picard was at a point where his two greatest psychological vulnerabilities -- the Borg and the prospect of parenthood -- were in synergy. Every time he took a step closer to happiness, the Borg showed up to threaten it once again. And that's bound to wear on a person, to create the fear that maybe he's cursed, or even that he brought this down on himself by tempting fate. Not rational, of course, but Picard had to make himself vulnerable and embrace his emotional side more in order to admit his love for Beverly and take the steps of marrying her and conceiving a child with her. And he's been through the wringer for months already at the very
start of the trilogy.
So yes, this is Picard at a less stable, more vulnerable state than we've ever seen him -- but it's hardly a mischaracterization, because it's justified by how he
got to that point.