I would say certainly the second trip was safer than the first, as the first trip ruled out lots of non carbon fibre related failures (e.g. the porthole)
I'm not so sure about that, pics of the wreckage being offloaded onshore show that dome being moved with a sling through the hole where the porthole should be. I don't think they would have removed that just to move it, especially before analyzing the debris.
The force of the implosion, as I understand it, would destroy the porthole in any case; it being not attached is not an indicator that it was the point of initial failure.
That is possible, it probably wasn't intended to contain severe pressure from the inside. Of course, being rated to only about 1/3 of that depth from the outside isn't reassuring either.
I would say certainly the second trip was safer than the first, as the first trip ruled out lots of non carbon fibre related failures (e.g. the porthole)