1) Overhead locker are designed to support weight, next time you fly look at the plackard you can find on the side.
True, but how many times do you see the overhead lockers jammed full with many cases that have a combined weight well in excess of the allowed weight. Some airlines, both LoCo and Legacy, do not consider this overloading of lockers by passengers a problem and it probably isn't unless something goes wrong. Hardly ever now but in the past with some airlines I have experienced every item of hand-baggage getting weighed. Then, of course we all buy litres of duty free!!