Was at my buddy's house last night for a bbq. He has been in the collision repair business for 35 + years. His job is to cut off all of the twisted metal and weld in the replacement pieces. He has to make sure it is structurally sound and all the panels line up, then it gets sent to the finishing guys. I guarantee he has welded on more cars in a year than Tony has his entire life.
Anyway, I asked him what he thought about this and he laughed. He said the only reason the factory didn't tie the subframes together was to save money.
Your friend maybe not be entirely familiar with old Mopar unibodies. IMO, the main reason was space/lack of floor height/ road clearance. I can't see using the rockers/door sills as compromised frame replacements saved much, if any money.
If it saved $10 per car, times how many millions of uni-body cars they made in that time frame, it adds up to real money.
At my company, they will spend an extra week engineering out two fasteners that won't have to go into the assembly. The material and time to install them saved is tens of thousands per year.
