"Unloaded" refers to the axles which I thought I made clear in my post. Even using your definition, my travel trailer will not skid tires on a dry surface. My boat trailer will not either unless the boat is in the water and the trailer is "unloaded"!
Don't tell me my bakes are defective because they are perfect. A 3500 lb axle has a 2"x10" drum which doesn't allow enough braking force to skid the tire. My 5000 lb axles have 12" drums and still not enough.
Please show us a video describing all you claim. As Judge Judy would say, "RIDICULOUS"!
Only logical thing I can see is that your truck brakes are weak or defective and you are seeing improved braking while towing. Might want to look into that because you might be a risk while not towing too.
Any yes, everyone new needs to know that ANYONE, including yourself, towing ANY trailer (loaded, unloaded, dry, wet, big, small, dry pavement, wet pavement, etc) will require MORE room to stop.