They way bigger issue than that is that he glued the metal rear section to the carbon fiber body. Both materials expand and contract differently under pressure, which is not what you want at 3 kilometer deep pressures, especially with multiple descends and ascends. That glue could never keep those materials together, that alone was a disaster waiting to happen

And people usually consider this when building a barn, doing plumbing in a house. The scariest thing is how can someone who doesn't understand this make a submarine. Real Crassus vibes.