It's not about asymptomatic cases alone. It's that people don't get tested, even if they have symptoms. There are according instructions not to test.So this idea that there is a large pool of unrecorded asymptomatic cases does not seem to be correct.
Re. the paper: I don't view that as representative, if you allow me to say. But interesting nonetheless! I do think that virologists are correct if they say people (especially children) can remain asymptomatic. That's pretty normal for some viruses, too, isn't it? It is not being said that asymptomatic cases build the majority (I think they do not). What can be observed, though, is that there is barely testing.
Edit: I re-read your post. Did I understand you correctly that on the ship they found 50% asymptomatic cases? That's pretty high. Sounds too high...