One really cant tell from that view if it is a swamped rib or not. We would need to see a view from the breech end, looking toward the muzzles.

This gun has a swamped rib:



Make note of it, ed.

Bill, using the logic used in the way you stated it, the purpose of a horse is to make horse shit. Yes, a horse makes dandy horse shit, but, the horse has other uses and purposes. There are multiple ways to achieve balance, involving the rib, or not.
I always thought the ugliest thing hung on a double gun was a tie, between beaver tail forend, and double beads.

Carry on.

Best,
Ted