Squeezer,
Whether that song is an "honorary shanty" (whatever that is?), much less whether someone "could be forgiven for assuming that the Farewell is the genuine article" (huh? Where does this come into play?), is not relevant to my comment.

The soundtrack is claimed to be of interest to people interested in shanties - this is the promotional tack. However:

1) It seems just ONE song on the entire album might be imagined as a shanty; and,

2) That song actually isn't a shanty.
3) Neither does it have the typical characteristics of a chanty.
4) Importantly, neither is it sung in the style(s) of chantey-singing
5) Less importantly, prior well-done recordings of the song are available.

The song, and its performance, stands on its own. Simply does not need to be framed as a "shanty." And because even if some (not I) consider the composition "honorary shanty" because "shanty groups" (sea music performers? folk groups?) have performed it, the performance is hardly "shanty-singing" and it makes up too small a portion of the album to recommend to shanty fans.

This is why I say there is no reason to undercut the quality of the performances and compositions. But if someone doesn't like being called out on the disingenuousness of promoting under the guise of shanty-singing, that is altogether too bad.