Thanks everyone. I do have one of the "stretchy" type straps. I imagined the limitations would be mostly the shear strength of the bolts used to attach the tow hitch to the frame.
Fortunately, there is no imagination neccessary. It's mechanical/structural engineering. FWIW, it's a daily exercise to size structures, their joints, inclusive of the bolts (size/number/thread/type). If you use a stretchy strap (to be clear post up what brand you're referring to), then ONLY use 1 in the pull. Do not link up 2+ especially with metal Drings. My earlier post I prefaced with "dead" pull to imply a static strap. Minimal stretch as the reference. When you get into dynamic, bungee cord like, there are other issues to be concerned about....like if the attachment point on the vehicle can handle the load, which would be GREATER compared to a static pull.
if your 4Runner receiver is like mine it is bolted to a cross bar of the framedand not a true load bearing hitch. I would be very careful doing any pulls especially side pulls.
So, what is an example of the hitch being load bearing in this context....? A cross bar (crossmember) rigidly connected to the frame is only an issue if it's not sized properly. It is in fact load bearing as that is the load path from hitch to the cross bar to the frame (going by your example). Are you saying the hitch is ONLY attached to this cross bar, rather then BOTH cross bar and frame?
What's the thing rated to tow? If it's strong enough to pull any decent size trailer, it'll be fine. You'd be amazed how much load can get put on a hitch when you hit a bump in the road while accelerating up a highway on-ramp.
The weight rating is not solely based on the size and attachment methods to the vehicle. it is also the suspension and drivetrain (transmission and axle gear ratio). The load of a trailer hitting a bump in a road are far below the magnitudes of recovery that we're discussing. Yet, it's still fair to use the tow rating as an equivalent to weight of vehicle being extracted...meaning MAXIMUM. Experience at hand plays into the rest of the situation as there are no absolutes with circumstances (terrain, position, weather, rigs, etc.).