At that depth, a crush death would be near instantaneous just like you said. They would have been liquified so quickly, their nerves wouldn't even have the time to even send a pain signal to the brain. Let alone the brain being able to process any stimuli of what happened.
Morbidly, that is the most humane death they could have had, as the other options were dying of extreme hypothermia from the water temperature, hypoxia from running out of air, or dehydration if they somehow managed to survive a day or two longer.
Thing must have been crushed in half a second under that kind of pressure, people inside probably literally didn't know what hit them, one moment you're alive, and the other you're not. Likely happened hours after they submerged, that glass porthole was definitely not going to withstand that kind of pressure for very long.
save