Bismarck was not a treaty battleship as the Germans did not attempt to fit her within the 35,000t weight limit. And she did not sacrifice firepower, the 15" rifles she used were literally the best naval rifles available to them. It's not like the German designers were sitting in a room saying "Right then, 15" guns or 16" guns? Well, we've used too much armor so I guess we'll have to settle for 15" guns" In fact, as designed Bismarck was originally meant to have 13" guns, so if anything her firepower was increased to the best available. The Germans sacrificed nothing, at least not intentionally.
I dont know how SODAKs armor scheme is "VERY good" when her belt was thinner than all other 1930s battleships and is also the only 1930s battleship with no internal longitudinal armor. Having said as much, her turret and deck armor is superb. You say Iowa sacrifices defense for Speed, dont SODAK and Iowa share the same armor scheme? Granted Iowa's belt is a whopping 3mm thinner and her main deck is 2mm thinner but Iowa's turret faces are 51mm thicker than SD's and Iowa's barbettes are 135mm thicker and Iowa's transverse bulkheads are 81mm thicker. In the end Iowa's armor advantages are pretty significant (51-135mm difference) where her disadvantages are hardly noticeable (2-4mm difference). Unless there's something I'm missing?
Iowa is hugely underarmored for her size. Infact, her armor scheme is quite poor for a ship that's 270m long. Although I understand her size and length was to allow her to break 33kts.
She also cannot defend herself from her own guns, but she's capable of defending herself from the 16/45 Mark 6. Just guns with the same capacity to damage things as her 16/50 Mark 7s will absolutely destroy her.
On the terms of Bismarck, her guns are too small for her size. This is due to Germany's inefficient loading mechanisms. She had the capacity for 16inch guns, but Germany hadn't made those yet intime for Bismarck's construction, but they had 15inch guns ready. (Since the Scharnhorst class was supposed to get an upgrade to the 15s, but looming wartime and the Z plan stopped that from happening.)
And what else are you missing? An totally inadequate armor scheme on Bismarck. Good upclose and capable of withstanding ANYTHING the British can since Britain lost the plot on Naval power after WWI.