I only watched the first half hour but there was the usual hyperbole and exaggeration I had rather expected, not to mention inaccuracies such as Titanic's after funnel blowing off steam and a shot of the Mauretania/Lusitania.
Seems that one set of people think the plates were too cold and thus brittle and another that they were hot and weakened. Maybe a bit of both, who knows?
But whatever the state of the plating, if 50,000 tons of ship with hull plating less than an inch thick and travelling at over 20 knots sideswipes an iceberg weighing hundreds of thousands of tons then the result is likely be be rather more than just a dent.
As far as speed of sinking is concerned, the further a ship sinks then the faster the rate of sinking usually becomes as the rate of flooding speeds up with pressure at depth and more openings drop below the waterline.
Colin