It still astounds me that nobody thought to question the most basic flaw of the geometry that a cylinder has at those depths, even the most awful engineer ought to know it's spheres only after a point.
It wasn't the shape, it was the choice of materials (carbon fibre) and durability.. it made the titanic depths 13 times (alledgedly)..
Of course, people choose spheres for a reason, but this guy would have still chosen carbon fibre and no doubt relied on his NDT acoustic sensors so you'd only know it was fatigue'd and about to go when it was all too late.
The reason he chose a cylinder was to allow groups of people to go in relative 'comfort'..
I know he was an idiot and it was a spectacular display of ignorance, but the fact it made so many dives whilst being constructed so 'wrongly' was actually quite impressive to me.