The wreck in the video you posted stemmed from a few things: not enough weight on the front of the trailer (primary cause of trailer sway), a heavy load (a BMW 850 Ci) on a trailer with an extraordinarily high center of gravity behind not-enough tow vehicle. The load floor of the trailer was above the tops of the tires.This is why having a big enough tow vehicle (and driving smoothly) is important... Highly exaggerated and ridiculous of course, but I wouldn't tow a 20' or larger trailer with anything but a full-sized truck or large SUV. No mid-sized SUV, or anything of that sort. No X5, no Grand Cherokee etc. They are too light and the wheelbase is too short.
It all matters. Wheelbase, axle-to-hitch ratio, wheelbase to axle-to-hitch ratio, comparative weights of tow vehicle and trailer, hitch type, how the trailer is loaded, etc.It isn't wheelbase which determines towing stability. It is the ratio between the wheelbase and the towing overhang (distance from rear tires to towball). A longer towing overhang gives the trailer a longer lever arm to waggle the tow vehicle with. Vehicles like the x5 have a small towing overhang, pickups have a large one.
This is why fifth-wheel setups are good: the trailer attachment point is between the rear wheels so their towing overhang is zero, so lateral loads at the attachment point have no effect on the vehicle direction.