I have no doubts that the aluminum would be less stout than steel of the same gauge, but in the real world, you'd likely have some sort of bed liner or bed mat in use. I have put the rubber DeeZee bed mats in most trucks I've owned, and there is no way you'd see the same type of damage using one.
Big difference between aluminum and steel is that steel can be bent back into shape, while Aluminum, when it bends, permanently alters the molecular cohesion at the damage point. Ask any auto body guy what they have to do to "repair" a dented Aluminum body panel... Steel, bang into place, rub-out with compression, and dent goes away. Aluminum, replace panel, as you will never get the dent to go away. That aside, the whole thinking by major auto manufacturers nowadays is to design and sell vehicles to the most profitable and biggest customer base.
40 years ago, that was (for pickup trucks) ranchers, farmers, tradespeople, etc who really really used those vehicles HARD. Today, the biggest portion of buyers is the bling bling, look cool while riding on heated seats, and wifi, for your kids in the back of the extended cab, hauling your jet skis or Razor, type of crowd. Those trucks never go near a work site where you'll likely be banged by Bubbas forklift, loading logs into your bed.
Big difference, and cause and effect, trucks now are designed with big towing capacity, not because you are putting 10k pounds in your bed, but because you need that towing capacity to tow your 10k pound toy hauler to Glamis, where the sides of the truck never see trail rash, or anything ever leaned up against them.