He was shown to deal with his rage in I Borg. And in Descent, they never encountered the real Borg.
This was the first time after Best of Both Worlds that Picard confronted the actual Borg collective again. Got haunted by voices in his head and nightmares. They attacked Earth a second time and he was again the ONLY one that stood between mankind and the Borg. And he was fighting a losing battle.
Well he was a bit out of character, but it's the "they invade our space and we fall back" speech that I found ridiculous. When did the Federation ever fall back in front of a Borg invasion ?