The savior thing - being saved is a known fetish of mermaids since for ever, as the story goes, they would appear and drive people mad about finding them and saving them from the seemingly desolate gloomy places they would appear in - mermaid needs to be saved and MC has the savior complex - as any Alpha for any pack would - it is in the blood of Alpha wolves to seek a pride and battle with anyone who would stand in their way to rule - driven genetics at their best.
The urges of their blood and their genetics permeating their still fragile yong adults egoes is what makes this whole game worth it.
Thing is that MC has no ties to Grace apart from the "she did let me fuck her a couple of times" and is
NOT part of the pack. As an outsider MC's Alpha Genes as you put it should not have activated.
King Fishy McSharkhead did not challenge MC for his leadership of the pack i.e. is not "in his way to rule".
Meaning the actual reason why MC wanted to save Grace was his helper complex alone.
Plus you as a player actually had no choice at all.
Even if for some reason your MC is not interested in Grace you
HAVE TO take part in this duel. And the outcome is also predetermined.
That right there is the main part of the complaint.