"People who have never experienced war can't begin to understand how the endless months of stress, punctuated by moments of sheer unadulterated panic combined with the loss of close friends and loved ones changes people.
I see all the characters dealing with PTSS in their own ways."
Some people it does, some people it doesn't. In this story it is apparently affecting everyone, including the goblins, and it seems to have started before the war actually got under way, when several of the characters were still in school the previous year, if not even earlier than that.
These characters aren't being written as if they've had fundamental personality changes because of the war. If they had at least that would have been a reason. But that's not how it's being written. It's being written as if up till the end of Deathly Hallows the characters had Always acted one way, after the end they had Always acted another, and it's impossible to reconcile those two competing thoughts.