You do realize that you made my point?
Troops traveling for a year in barracks-style accommodations while crew get cabins? Mercenary troops relegated to being stacked like cordwood as their living quarters while other ships crew get 2 man cabins? Even for volunteers this will engender poor morale amongst the cannon fodder.
The interpretation of the rules like this runs smack into the reality that such things are highly unlikely to exist. Bad rules are just that - bad rules - and when they are contraindicated by common sense they should be revised. Troops assigned to serve aboard a ship should have the same cubeage as anyone else of their same rank. Troops being transported by the ship (temporarily) should be the only ones occupying barracks.
Assigned and transported by are two entirely different issues. My logic works quite well because it's, yanno, logic.