Everything is a tradeoff.
A true "flat" or "ute" bed is meant to be used for larger loads and be easy to load and unload. The large flat load floor is a much bigger advantage than the small increase in CG height. Especially when made from a lighter material.
Almost any mod increases CG height.
Lift
larger tires
roof rack
roll cage
bed rack
Flippac
RTT :Wow1: say it ain't so!
on and on and on
Its all a balance of convenience vs. performance.
If you design one out of aluminium with large drawers between the wheels for recovery and camping gear, tool boxes on the sides between the cab and wheels, and mount an RTT flat to the "load floor" you could lower the CG over a similarly equipped regular bed, and definately a similarly equipped SUV.
It's more personal preference I think.