Who Owns the Airplane Armrest?

I think the writer hasn't been on a large plane. The biggest one that I've been on had the typical 3-seats on the sides, but 5 seats in the middle rows.

On that plane, the problem pointed out in the article appears again, because there are 3 people who battle it out in the 5-seater rows.

I only image in that case, thr middle person gets 2 arm rests, and the neighbours lean away towards their closest aisle.