The Coast Guard report section “5.6 Insufficient Understanding of Carbon Fiber Material Properties for Deep-Sea Applications” addresses your arguments.
Yes. It can be safe. The problem is that its crystalline structure can fail instantaneously without any ability to detect beforehand. In this case the sub was likely improperly manufactured and improperly stored and damaged from previous dives and from transport. The company “planned” to inspect but as no non destructive testing was possible, they didn’t bother.
There is a YouTube channel that anaylzes the core problem in depth. Compression vs. tension is really a red herring because in a closed convex structure compression somewhere is tension elsewhere. The real problem is the carbon fiber maxtrix was wapped around the epoxy filler without tension like paper mache. So it had insufficient strength and non homogeneous strength. The sub was built up like an onion. Concentric layers of carbon fiber epoxy thermoset. I think it was something like 5 layers. Anyway because the layers were not wrapped tight before curing there were ripples in the surface of each layer. Subsequent layers were applied after sanding down high spots and applying a wrap of double sided adhesive tape between each layer (no joke). So not only were the carbon fibers not pretensioned but also they were cut in hundreds of spots. This is somewhat like if one were to pour layers of reinforced concrete by throwing a bunch of loose rebar in a hole, pouring concrete over it and then cuting pieces of rebar that stuck up before applying the next layer after putting a layer of plaster over it. For carbon fiber composites and concrete to be strong tension bearing elements need to be able to bear tension. If they are loose in the matrix or cut the composite will not be strong. Thus carbon fiber was not the problem but rather its manufacturing process. Anyone who has ever done drywall joints or autobody can understand the problem. It doesn't take an engineering degree to understand that if you wreck the tensile components of your composite it will be much less strong than if the composite is laid down properly!
Yes. It can be safe. The problem is that its crystalline structure can fail instantaneously without any ability to detect beforehand. In this case the sub was likely improperly manufactured and improperly stored and damaged from previous dives and from transport. The company “planned” to inspect but as no non destructive testing was possible, they didn’t bother.