Dorian was quickly convinced, not only because Karman's argument made sense, but more importantly, because he was quite superstitious. He knew well the importance of respecting the "feelings" of someone more successful than himself.
This had nothing to do with professionalism; after all his expertise, hadn't he ended up with a huge debt and was almost driven to death by the Mori Family?
The choices of successful people often come with a blessing of luck. By following the footsteps of such people, one may not reach great heights, but it does help to minimize mistakes.
The battlefield is inherently fraught with unexpected events, and no one could guarantee what might happen during the actual operation, making "luck" especially important at that time.
Sea evacuation was indeed an option, and Dorian easily compromised because he was ordered by his boss to command this attack.
