Even though Hal is a smart guy. Many of us already realize that there are problems with safety boxes, and surely we do not know the details of exactly how Hal saved his keys in safety deposit boxes, but that could be one point of failure if that might have had been the ONLY place that he had his keys and/or other instructional information related to his bitcoin.
Good point, but the sad truth is you have to store your private keys somewhere. If it's a physical location (be it for paper wallets or electronic devices) it'll always bear a risk of someone unauthorised getting their hands on it.
That could be mitigated by splitting it in 2 or more parts and store each separately. In Hal's case - he referred to one box, but at the time he passed away (2014) nobody really knew where BTC will go, so, I reckon, at that time it was probably not the most valuable asset of the inheritance. And we all tend to apply level of security proportional to the value of what we try to secure.
In the end, it is likely a good thing to recognize and appreciate the splitting of keys and/or the splitting of information.
And, sure sometimes these days private keys might be recognized and then figured out how they might be applied to some kind of a wallet (without even having instructions).
We cannot exactly know the size of Hal's stash, but it is thought to have had been pretty large, even in 2014 terms. ..and yeah, may not have been completely disclosing the details of how his keys were being secured and that might be part of the reason that I suggested that it might not have had been a good idea to be quoting that message from Hal in regards to how it appeared that he may have been holding his keys for his family members.
For sure, your point about the level of security attempting to somewhat match the present or future value of the stash or maybe making changes to the way that the coins are secured if the stash value size changes are surely valid.
Many of us who have been into bitcoin for a while have likely experienced some level of changed concerns, and for example if someone had bought $10k worth of BTC for $300 each (which would have been around 33 BTC) in 2014 or 2015, may well have ended up surprised as soon as 2017 regarding how fast those values were going up perhaps 50x or more... so the price rise of 2017 may well have incentivized additional security measures or changes to then practices...and even a 5x or 10x change in value may well end up with similar kinds of concerns to change security practices.