When I flew the MD80 with it's 2-3 seating I used to ponder this.
I came to the realization that the seating is not asymmetric at all when
you think about it.
Its the Aisle that's offset from the centreline, the closest seat to the aisle on the right is actually right in the middle of the cabin with two seats on either side
'balancing' the lateral load.
So the only off centre load is in the aisle itself, not much of an issue.