It has been two years but we used to pick the back of the plane when our son was young and yes, there were always empty seats even on flights that should have been sold out (Caribbean destinations on peak weekends for example)

I don't remember annoying lab traffic. I do remember getting good service from the FAs but that may have been the result of the blondy boy charming the crew, he has been a chick magnet since the day he was born.