BW its wise to be skeptical so no worries on questioning anything.........
Again we have to remember we're dealing with body-on-frame which is key to this discussion. In unit body vehicles its fairly easy to see the effectiveness of that design by viewing actual collision damage and learning what bodily injury was/was not suffered. In the case of E-Series or any body-on-frame its a safe bet much of an impact's energy will ultimately will be transferred to occupants, the relatively few crumple zones doing little to absorb or deflect that energy.
Air bags in their various forms and locations, lap belt pre-tensioning devices as well the height of an E-Series van is beneficial because most vehicles on our highways don't sit that high off the ground. When another vehicle hits a van the lower one tends to strike at about frame level----because we sit higher up we're somewhat spared a full frontal impact, that which would impart the largest energy to the occupants. (All this assumes two things: a.) all occupants are properly seat belted in place & b.) colliding vehicle isn't same size or larger.)
When we add front and/or rear hitches which are tied into the frame they become battering rams of a sort even though not intended to act in that manner. The photo shown here seems attached to the frame both fore and aft of the crumple zones, essentially bridging them which effectively negates or greatly diminishes their purpose. However because an E-Series frame is relatively soft a head-on collision would still find the frame deforming due the energy transfer. When/if that energy "travels" far enough through the frame where it reaches the body mounting bolts those would be affected, either sheared away or at least displaced to some degree.
We all have to keep in mind despite a van's size its not much more than a paper-thin shell in which we sit and trust won't be in a severe crash or roll over "event". ( I just LOVE PC conversations, as in: So sir please tell me how you came to Sh*t yourself? Wull officer---I was involved in a roll-over event......."
) Head on crashes have huge speed differentials, rear end collisions tend to have less and side impacts are almost 100% affected by the speed (and to some extent the size) of the other vehicle. These conditions and circumstances all affect how much energy will be absorbed by the bodies inside.
Should a van land on its roof (from a fall or very severe roll over the A, B & C pillars would be effective one time---subsequent roof impacts during the same roll over event would find them exponentially reduced in structural integrity, basically collapsing and no longer able to protect occupants.
Keep in mind we're talking worst-case scenarios so don't take this as me saying vans are inherently death traps---size matters in this case too.
Anyway hope that's not too boring but helpful in some way.