score:5
I checked the Japanese text, which is as follows:
世界の三馬鹿「ピラミッド・万里の長城・戦艦大和」
I can confirm that this is mentioned in many histories of WW2 as a joke which was whispered between Navy staff. One notable source that comes up on Google Books is a 1965 biography of Yamamoto Isoroku by Agawa Hiroyuki.
Because it originates as a joke, the point was to astonish and there was no explicit reasoning given. I suppose the intuition would be that it was a very expensive project which did not produce the desired result of victory in war. In the 1960s, the same joke was told but instead of the Yamato, the third example was the shinkansen, which kind of shows the mentality of the joke teller.