Hi Tim,
I agree with you on form following function. The major reason I question the handle design is the swelled grip, not the crescent pommel. Just for comparison's sake, Tribalarts.com has a sawfish bill sword made by the Batak (I believe), and it has a straight handle with a wrist cord.
So far as parade items.... It might be possible, but it depends pretty critically on the age of the piece. Assuming once again that it came from the Torres Islands, their history is fairly interesting. They were colonized and missionized around 1860-1870, were finally given a bit more freedom around WWI, and staged a peaceful strike/rebellion in the late 1930's.
The problem is that both of us date this weapon to around the turn of the 20th century. It's pretty obviously old, but if it was made in the Torres Islands, it was at a time when they went to Church every Sunday and the kids went to mission school. If it was less than 50 or more than 130 years old, I'd be thinking more strongly that it was native made, especially as artwork as you suggest.
Nowdays, the Torres Islanders produce some neat artwork (admittedly, I'm partial to Oceanic art in general), and my impression is that this is a post-WWII phenomenon.
This all assumes that it came from the Torres Islands. If it came from the Massim (eastern tip of PNG and related islands, including the Trobriands), then you could make a stronger argument that it was native made, although I'd still disagree
F