I think you're missing the point. When making these design decisions, you have to ask 'what can go wrong, and what is the implication of that?'. In your example, you can replace the controller with ease if it breaks, but you can't do that when you are underwater at 4000m below the sea level. Therefore it should at least be designed to be more durable and redundancies should be built in, say a basic console with physical buttons.

But anyway, this controller debate is probably irrelevant anyway. I think it's unlikely to have been the cause of the problem here. Hope the sub is found soon so we can know what happened exactly.