This was the video in question. I’m not sure if it was filmed before or after the patch that fixed the 155mm ammo being fatal (which weirdly enough, they’re fixing again this update?). Regardless, you can see at the timestamp 5:55 that they only hit on and right under the barbette of turret no.2. You can also see the single fire pillar that’s characteristic of a shell room explosion. And you can see at the very end of the video that Yamato died to some mysterious “explosion” even with 0 shells in the main guns. But those should hopefully be fixed by the next update.
I have a replay of me detonating a Yamato using Mutsu with what seemed to be a non-pen, but I think it might be a bit late now to report it since we’re so close to the next update. We’ll have to see if that’s still an issue.
As for Soyuz’s SAP… Let’s just say that the Iowa’s 16in HE have a charge mass ratio of 8% and Soyuz’s SAPCBC is 7.9%. A 0.1% difference. Now of course the SAPCBC shell is heavier, and has a cap and base fuse (though the shell is also very long and gets very thin walls), but you’re telling me that that’s enough to give it 87% the performance of a true APCBC shell?