Back in February 2009, JWE had this to say about ship maneuver.
... Maneuverability depends, first and foremost, on how the game engine uses the values in its calculations. There are several calculations, for several different conditions, so maneuver values have to be suitable for all of them. Tweaking for one will likely break the other 3 or 4.
The maneuver values lie on a functional curve. Basic values are developed from the speed/size ratio, but the plot is not linear. Actual cruise speed is important, cruise vs full speed differential is important, hull K factor (displacement vs waterplane) is important, speed-power and power-length ratios are important. Then the engine takes over and the calculated values are scrunched into the processing box by a functional fit.
A ship having the same speeds, but 1/3 the size of another, will not have 3 times the maneuverability, ships having the same size but different speeds may have the same maneuverability because of hull configuration, list is endless...
I recall it being said that Titanic had what was really too small a rudder to enable her to turn adequately (might or might not have been a contributing factor in her demise). So certainly design issues beyond raw size, speed, etc. as you say.