I know what you're saying about the Mains. They do have some wonky spreads at times. I've managed a 30-31% Hit Ratio in Randoms but a 44% in Coop. I do tend to play pretty aggressive in Coop though lol.
I went with a dedicated captain pretty much from the start and dropped a 19 point in her. Specced PT, PM, AR, BFT, AFT, ManSec, IFHE. The only change I made was switching FP for IFHE after the first 10 games or so. The damage with IFHE went up noticeably. Tier 6 BBs coming at you Bow In? IFHE doesn't care and lets the 127's pen their Bow. Plus the Cruiser Damage went up.
On Manual Secondary Accuracy: I compared my Secondary Hit Ratio in Coop between Bismarck and MA. I was able to start with a full Secondary build on Bismarck as soon as I got her. 164 Games with Bismarck the 2nds Hit at 29% and have killed 51 ships. Only 64 games with MA and the 2nds Hit at 46% and have killed 48 ships. I just cannot get over how accurate they are.
All in all she's pretty much my favorite ship for now.
Good luck with yours!