Behind the Bastards did a pretty great two-parter on Stockton Rush, and how a) he completely shit the bed while ignoring all the super-deep-exploration experts, and b) how nature was totally telegraphing to Rush and OceanGate that this submersible is totally not doing it and will end in a spectacular tragedy, only no one else will be down there to watch but the fishes.

The controller wasn't a particularly weak link, though for safety's sake I'd want there to be a redundant spare, and it set up for plug and play. But higher on my priority list would be things like integrity monitors and an emergency way to open the sub from the inside (the hatch was bolted from the outside, and there were no emergency exit measures.