I cannot understand how this could possibly happen in the open sea. A contact is picked up miles out. It’s course and speed is computed and watched for changes. A full steaming watch is on duty: Conning officer, Radarmen, lookouts (forward, aft, port and starboard), a quartermaster records a log of all events and orders given on the bridge. You never allow your ship to come within 1000 yards of yours. They knew where the cargo ship was from more than ten miles out and tracked it constantly. If the captain was on the bridge, that means he was woke and called to the bridge. There is much more to this than just an unfortunate collusion.
The Captain, from stories already reported, was not on the bridge. He was actually in his quarters, and suffered head injuries during the collision.
I agree with you about all your other assumptions. As I pointed out in an earlier post, the Combat Information Center would've also been watching all surface activity, and would've been in communication with the bridge about the proximity of this vessel.
To me, a "ramming" of the destroyer seems unlikely--it seems as though the destroyer may have misjudged a maneuver in order to cross in front of the container ship, but failed to pass soon enough. If such a move occurred, it demonstrated poor judgment by whomever was driving the destroyer at the time.
Multiple articles that I've seen have reported that the captain was in his stateroom, not on the bridge.
On Navy destroyers when I was in (many decades ago), the captain's underway stateroom (or 'sea cabin') was at the bridge level, just a few steps directly behind the bridge itself. Apparently, on the Fitzgerald, it's off to the starboard side where the collision damage occurred.