I was super confused as well by the "body needs to flex or the spot welds will work-harden" comment by Uncle Tony. Things work harden by moving that's why it's called WORK harden, pretty sure he's got it backwards...
Also I'm a huge fan of UTG but after watching a lot of his videos it's clear he doesn't have a background or interest in making cars handle, just old-school drag racing. Which is fine but not everyone is building their Mopar for that.