If they did that then Yamato and Musashi would be seven and a half foot tall giants.
Specifically, the average male would only be barely taller than Yamato's belly button, while even Ooyodo would be about 6' 3" tall. Also Katori and the destroyers would be teensy.
Specifically, the average male would only be barely taller than Yamato's belly button,
Not quite that silly, the Yamato's would be by this reckoning about 2.56 meters tall. Average shoulder height is about 80% of total height and elbow height is about 60%. That's about 2 meters and 1.55 meters respectively, so an upper percentile male would reach about their shoulder and an average one (175cm) would reach their bicep. This height is within the limits of males with gaintism, but is nonetheless unbelievably huge and never really implied at any time.
It's also worth noting that using this system the Cranes would be basically the same size, Kaga only slightly smaller, and Akagi and Taiho being slightly taller. Yet there was never any real implication that the carriers were even just unusually tall for women (as you sometimes see with the Yamatos).
Still the Americans would be even worse Saratoga and Iowa would both be basically 270cm, Intrepid would 'only' be 266cm.
Also Katori and the destroyers would be teensy.
This would arguably be a bigger problem then a huge Yamato and carriers. All the destroyers could basically be considered to have dwarfism. Most (Fubuki, Kagero, Yuugumo, Asashio) would be like 1.2 meters tall which is about the average height of a six year old girl. Shimakaze and the Ducks at about 1.3 meters would be giants at very slightly larger then an average eight year old girl!
All this was why the entire idea of m=cm was stupid and clearly wrong from the very start.
This was why the entire idea of m=cm was stupid and clearly wrong from the very start.
The problem isn't so much that height cannot be proportional in some way to length, just that direct linear scale creates a bizarre effect. One could always have a sort of fudged logarithmic scale or even ordinal scale rather than a direct linear 1m length = 1cm height conversion. That is to say, you set the two extremes based upon the longest/tallest and the shortest ships so that the tallest are 6'6" / 2m and the shortest are 4'6" / 1.4m. Considering that some of the shipgirls actually are portrayed as middle or grade schoolers, that's within the appropriate realm.
As it stands, the vaguely consistent idea that class relates to age tends to make smaller ships shorter, and there are some ships where longer classes are taller shipgirls than others within their class, at least in fanart, but it's just not consistent. (RJ being frequently portrayed much shorter than she would be in an ordinal scale conversion, for example.)
