I don't know but it seems the angle could have been even more acute than what you allow. And if so no mystery as to why an "abrupt change in course". The Fitzgerald's momentum, possibly reaction of helmsman to steer away from what just hit them could all be reasons for that turn.
Looking at the rip on the Crystals bow (see below) and the fact it seems at this point to extend only down the one side and further given the nature of the structure in the stem area of a ship like that with breast hooks, stringers and generally dense framing what on the Fitzgerald is strong enough to create that damage? Perhaps the hull / main deck edge?
Looking at below, perhaps where marked was initial impact of the topsides (the bulb having displaced/ cracked / tore / penetrated the hull below where we can see. Looking at the "folds" of the topsides in way of / just above main deck this could have been the path of the tear in the Crystals hull, this stronger section of the Fitzgerald's construction acting like a can opener. Tear-fold, slide, tear, fold, slide. Many may be picturing that bulb buried in the hull but it wouldn't take all that to present serious flooding problem. One good crack/tear along the side as the Crystal pushed the Fitzgerald off out of its way would be enough allow flooding enough they had to fight to save the ship.
The nature of the damage to the Fitzgerald's topsides above this line is not surprising given the flare of the Crystals hull at the bow. And if the angle was more acute than you propose might account for the swiping look to it.
With what we know to date it does not seem likely to me the Fitzgerald was not making way or "stopped" (in a traffic lane?) and in fact looks more like it was moving pretty quickly. If the USN has anything like VDR's that will settle it but in the meantime if it was moving at a good clip and impact angle was far less than 90 degrees this makes sense to me why no "center-punch" in the Fitzgerald and why no need to back out of her or some other elaborate explanation for becoming dis-entangled. Again the momentum of the collision and perhaps deliberate helm commands to get away from what just hit them. Then again if it was stopped would that make a difference (nature of damage-wise) if the blow was more glancing?
Likewise I don't find the speculation of the Crystal's track after much of a mystery either. Until the crew of the Crystal interviews are published we will not know what they thought they were facing and their thought process in getting their ship's situation stabilized. Wake crew, avoid other traffic, damage inspections, return to scene. Not sure what is behind that speculation other than to cast aspersions without enough facts or evidence. Sure the USN has been subject to the same in this thread though.
But these things are really the least interesting part of this event. Situational awareness, keeping a proper lookout, bridge resource management, whatever you want to call "it" will be determined as faulty on both ships. Someone will say why and someone will say how to avoid that in the future and mostly things will go on going as they are. If you've read this far all you can say to yourself is "be a better seaman, be aware of assumptions, look, listen, avoid complacency" and on and on in similar vein re-learning the lessons of our individual and collective past mistakes and close calls.