Duty belts work best when they are used with belt keepers to anchor them to the pants belt. I've seen folks with only a holstered handgun and spare ammo on the belt bring an unanchored duty belt up to their armpits before the handgun started to come out of the holster. (Good holster retention but not helpful.) You apparently know and understand this.
That being said, a good reinforced gun belt can be worn over the pants belt in the same manner. It's just a little less obvious.