carbon fiber is great in tension, i.e. a compressed air tank, or COPV
carbon fiber is much less great in compression, i.e. OceanGate
Also the OceanGate construction process was bad, even for carbon fiber, because the CEO didn't listen to actual engineers.
At this point I look at wikipedia what happened to the submarine bamboozled mentioned. Ooops. Heh, the pressure of water is as evenly distributed as can be. Seems my background in watersports is not enough to moonlight in material engineering.
Fry: "How many atmospheres can the ship withstand?"
Professor Farnsworth: "Well, it's a space ship, so I'd say anywhere between zero and one."