I will agree on looks. To mean the German ships always looked, well, mean, which is how a warship should look.
Yes the Iowa only had a 1in advantage in shell diameter, but look at the stats. Iowa's shells were nearly 1,000lbs heavier than Bismarck's and that is a huge difference. That equates to a broadside salvo 10,000lbs heavier. A huge advatage to Iowa.
That being said, human skill and luck are probably the two most important factors in detemining the outcome of any battle in any arena. Still, Iowa was the better ship.