Trying to con people into thinking HEPA filters made an aircraft cabin safer always was a dodgy call.
Yet no cabin crew contracted COVID? Do they not breathe the same air? Do they not move throughout the cabin, thus being much more exposed to multiple zones?
Perhaps the HEPA filters were doing more than you think. I would say the infections were more likely caused by contact transmission, given the number of cruise ship passengers on board, and the small number of non-cruise passengers infected.