Functional safety standards follow the principle of “eliminating _unreasonable_ risk”, not to reach “no risk”. So, on the one hand he is correct, at _some_ point you don’t gain anything with endless design improvements and testing. On the other hand, he’s used this as an excuse to not follow the processes functional safety standards provide because it’s expensive and time consuming - which is the problem.
Such processes would dictate that you have requirements and that all of those requirements have been tested. So, if the requirement is that “The submersible vehicle must maintain structural integrity at pressures equal to those at 4000m below sea level.” then there should have been a respective TEST(s) to validate that requirement.
Apparently, this wasn’t done, which makes him reckless. Now, this isn’t a ‘mass produced commercial vehicle’ - but I’d guess this still puts him in serious legal trouble.
Only if he gets out of the sub alive.