Even with a full frame vehicle the body adds rigidity against torsional twisting. The last glue job I fixed was a Suburban that had a roof put on at another shop for hail damage and it was leaking water. The front edge of the roof was partially separated under the urethane set windshield and I found a few places down the sides where an epoxy type seam sealer had cracked. I'm not really sold on the epoxy seam sealers either. They're fast to cure and you can paint over them in no time, but seem a bit brittle to me. I've had to re-do a few bedsides where I had done the job. When the stuff first came out everybody used the glue and then the comebacks start coming including ones that have been hit a second time after being glued together. The 4 tacks or plugs on the corners they recommend just isn't enough.
It's what's not in the video I posted that scares me most about they way they did it. Also in the directions Blu posted directly from 3M where you glue the leading edge of the quarter to the inner structure in the door jamb. The quarter helps support the striker along with a small reinforcement that sometimes comes with a new quarter. Yup, just glue it all together and it's good by the manufacture's directions. Glue is one of those things I get pretty adamant about like Blu with his repairs "What about f'in next guy?" Because the next guy might be on the way to Dairy Queen with his kids in the back seat when he gets nailed and the door becomes un-closed. A Pro-Spot machine is the only one I've used that can generate enough amps and clamping pressure to pull off the weld/bond method. The stuff sounds great on paper but it just doesn't really work like they claim, it's widely misused and really causes some serious safety concerns. I would bet that when you pulled those loose bedsides off there was plenty of corrosion in the seams already.