I agree with you on the importance of the changes to the charging cycle, and the relative unimportance of the box - see my post 1358 on this thread, about a month ago.
But the changes beg the question: why weren't they done before the aircraft was launched? What do we know now that wasn't known then, except that the batteries do catch fire? If the root cause of the problem really is unknown - and it all comes back to this statement - how do Boeing know that the changes are adequate?
Certainly playing with safety margins will reduce the probability of practically anything bad happening. But if you don't know what you're aiming for, the amount of reduction you actually get is just guesswork - suck it and see, as I admit to having done myself a number of times in an earlier life. I really sympathise with the Boeing, Thales and Yuasa engineers, as I have been there. But then again, I've never worked in anything as safety-critical as aviation.