He makes crap up as he goes, always has which is why I don't watch him; absolutely can't stand him not to mention the fact that he is an idiot.
I put SFC in pretty much everything I have and it makes a HUGE difference.
So according to these 2 geniuses the cars don't need SFCs and/or they have enough? If you have spent any amount of time actually building some of these cars you will see evidence of twisting and sagging (just look at the door gaps on many vintage Mopars); not that it is detrimental per se, but its there. Dipshit from GYC is completely wrong and just wanted to upstage the other dude and try and sound like he knows what he is talking about (which he doesn't).
As far as UTG goes, another "make crap up as you go" type guy. He is saying that the cars need to flex in order to keep the spot welds from work hardening...….. hmmm, ever flex a piece of metal back and forth for a while... it fatigues and fails (i.e. breaks). Sure a unibody car does absorb some of the energy through the body under acceleration, hard cornering, etc. but this is not a good thing or something I believe was intentionally built into the cars; it is a by product of the build design which evolved to reduce the time it took to build them and the cost of building (increase revenue). His hypothesis is that by adding SFC's it focuses all of the torque energy into one small area of the car... hmmm seems kind of like that would be desirable in about every scenario I can think of.
American cars have gotten a lot of crap for not being able to take corners and handle over the years and this is not without reason; in general most we never built to do that specifically and unibody construction did not help. If the question is whether or not to install SFCs, the is up to the owner but I install them in pretty much anything that I am going to put some HP into or want to handle.
Be careful of who you listen to and believe; both GYC and UTG are good examples of who not to listen to or at least to believe without collaborating information/evidence.