>>>>>I can't really imagine a scenario where you have no [exit row] seat mate on an 330 though...

I think I had it like once. But I actually HOPE that my seatmate in the seat next to me in the exit row is taken well in advance. That's because when it is taken well in advance, then it is taken by a well-travelled elite member, who knows all kinds of minute detail about travel etiquette, and might actually be somewhat normally-sized.

When the seat gets taken on day of departure, it is more-often-then-not taken by somebody huge. Huge LONG is one thing, and is no problem, but huge WIDE is another. On two occasions when I wound up with a seatmate who was huge WIDE, I managed to dig the elbows out of my ribs while trying to sleep, and then place the straying elbows (attached to the wide person who was snoring) back in the assigned seat, and then raise the tray table into a straight upright position, then jam some material (sometimes part of a jacket) into the armrest below the upraised tray table so that the tray table could not go back down (even by an FA who tried again and again to force the tray table down).

When the tray table is jammed into a raised position like that, it benefits both sleeping passengers, actually.