If you can't stand not using full displacement, go play a sub since all of those use (nearly) full displacement.
Outside of AW ships almost all other ships have a lot of displacement going unused. And they do that to maintain speed.

So not using full displacement is the right thing to do for BBs? I know SN armor is not the strongest and the maximum I could put on my Stalingrad with full crew is only 4inches + and with less than 50 bulge, but that is definitely better than none if I could afford it without that much speed penalty all SN BBs face. Even with that setup I still die to 4 torps from SSs within a salvo, not to mention I do not have the OH speed to even evade it in time.

I really have to doubt your statement of "almost all other ships have a lot of displacement going unused", because almost everyday my Stalingrad gets sunk by an L2 with 11 inches or more deck (my 16' shells gets bounced at max angles) charging at 42 knots and firing his nearly blocked 18' at me. We already lack the firing power (due to inconsistent spread) and yet we could not even run from being sunk in less than 2 salvos.

The present state of SN BB play is pretty much solely dependent on teammate CVs providing air-cover and other BBs drawing enemy fire so that we could SLOWLY move into our range and make a shot and SLOWLY turn away in hope that we could move out of the enemy range before being spotted and shelled to death.

I have not played SN BB5 yet, (due to the slow and pain experience of running an SN BB4 that feeds almost all other BBs in the GB) but based on the feedbacks I've read in the forums, that of the nerf of BB5 lvl100 guns and the even slower moving speeds, I am just like any other SN BB players that have lost hope and motivations of grinding through.

If you have observed carefully, the number of SN BB5s in GBs since the new patch has dropped substantially. That surely explains something.