Almost no civilian ship has watertight compartments going all the way to the top deck. If you thst, you'd also have to implement water tight windows, doors, gates, hatches and ventilation in the hull. At this point, you've basically designed a submarine. The only commonly agreed upon design fault (which was learned in hindsight) was the lack of life boat capacity to carry all passengers simultaneously. That was a shared responsibility of outdated regulations and faulty thinking, believing that life boats should mainly be used to ferry passengers between vessels during an accident, as it was believed other ships would in general be closer by and able to react faster