A straight axle is about the only thing that moves straight up and down on a vertical plane. If you have independent front suspension it moves on an axis, hence the reason camber changes with lift/lowering, it rotates. A center arm on a tube chassis truck is different, but that's not what were discussing. A long arm kit on an oem chassis changes the extent to which it rotates, but it's the same concept. When you drop the rear, especially as drastically as some guys are doing it, it changes the entire suspension geometry. Drop the rear 3" and now the front springs/shocks rotate rearward and work on a decline axis rather than a vertical one. Not only do they not function as well as shock absorber but it also causes issues with braking and cornering.
A real prerunner gets it's additional front wheel gap from widened wheel arches, not from saggy ass suspension.
Frankly, I'm not sure what you're even arguing about. You suggested rear-low made it easier to load the bed, well, that's stupid. To only raise the rear 3" and the from 6" isn't helping anything and definitely isn't why guys do It.