From what I can tell the lawsuit (which is against Ocean Gate, not Logitech) is really just calling out the controller as another example of willfully negligent behaviour.

You’re certainly correct that the actual cause of the failure was the carbon fibre hull. Just a terrible idea on so many levels. Carbon fibre, by its nature, is good under tension, not compression. It was never going to function well as a pressure vessel underwater.

There were a litany of terrible decisions made by Ocean Gate, such as not tethering the sub, because it was cheaper to launch it from a towed raft, but none of those bad decisions ultimately mattered once that pressure vessel failed. Those people were dead so fast that, to quote Scott Manley, “You go from being biology to being physics.”