I am really surprised this didn't kick up

Great discussion here, I'll just throw a few more thoughts out there. Fifty years ago, every American car manufacture that I know of built unibodies the same way, without frame connectors. I'm guessing that was just the engineering school of thought of the day. Subframe connectors most likely came about because problems, or perceived problems, that people were having caused the the factors mentioned above. So much has changed over the last 50 years, that it is hard to keep track of it all. First, engineering has been able to increase the strength of modern vehicle both metallurgically, and structurally. Todays metal is both lighter and stronger. Also, the modern unibody is strong enough use on SUV's which weighs a lot, and have higher centers of gravity which puts a lot more load on them.

I think it interesting how the aftermarket has tried to improve our cars. A company like Hotchkis uses connectors, but QA1 does not. QA1 sells a tubular K member, but Hotchkis does not. Neither of them sell torque boxes, core supports, or under fender supports, but US Car tools and XV racing does. Everyone of these companies have some sort of engineering behind their product. Whether or not one is better then the other is hard to tell. The one solid case for connectors the David Rea brought up in one of his recent videos is when a k frame is that uses coil over shocks that do not connect to the factory shock towers. His point was by doing so, that style of K member put more stress on the car because it no longer connects to the factory engineered strength of the shock tower and torsion box. It seemed to make sense to me, but who knows. That said, I know some of the aftermarket bolt on front members used in it the early Mustangs and Falcons broke off at the mounting points because they did not connect to the towers. Anyway, food for thought.