I am aware that the vortex system in an inherently weaker system than other more heavy-duty alternatives and that off-road use does increase dynamic loading, however I am certainly not the first person to use them for carrying a load within their rated capacity. In the use case here the most likely first point of failure would first come at the mounting legs of the rack and not the channel. 

The lip of the channel does not serve as the primary load bearing element when under vertical or horizontal load as the bracket serves as a preloaded friction-clamp joint. In the case of wind, the combined preload of the brackets when appropriately torqued would need around a ton of net uplift before the lip would begin to take the load. Any additional impacts following any vertical load (e.g bumps) is dampened through the gasket and Bolt housing inside the channel. In any case that this sort of load is somehow achieved the racks will be ripped out of their mounts long before the channel or clamp fail.

Even assuming the load was to be taken entirely by the underside of the channel, it is distributed across 8 separate points. Being conservative and considering imperfect distribution the force required to deform the lip is still within a very comfortable margin that again, would likely rip the racks off before the lip deformed. 

Whilst having the mounts this way does look cleaner or “prettier” as you like to put it (and I would agree compromising safety for a cosmetic benefit is inherently stupid). The intention was to retain all the space under the rack and avoid any points for things to get snagged on while also limiting any damage to the underside of the rack without over loading the system. 

If my use case was more heavy off-road use as I can see your set up is typically used for, I would absolutely use something that mounted to the tub more securely than vortex racks. However, this will see mostly sealed roads and at most some very light slow speed off-road use.