The RC F has more chassis reinforcements in the rocker panel area because the RC was designed to be a convertible...but never happened. The RC chassis is a mix of 3 different chassis...in which is behaves on the track the way it does. It's front heavy and is prone to understeer. TVD is just a mask to cover up the chassis' shortfalls.
I expect the IS 500 to perform better than the RC F...with or without a transmission oil cooler. Don't discount the fact that the IS 500 F SPORT Performance is not a full blown F car. And with the new Lexus Driving Signature, it will surely have better suspension and steering feel than the RC F. Proof is in the 2021 IS 350 F SPORT Performance. You should experience it for yourself. The RC F is now a 6 year old car. Sorry.
LIke I said, you continue to misrepresent the facts. The RCF also has a 10-point brace in the rear that the IS500 F-Sport does not have. It also has shock tower braces in the front that the IS500 (or the GSF) did not have. All of those chassis strengthening were done in order to make it worthy or racing homologation, which is what it was built for. Those are Yaguchi's words. You are saying it is front heavy, but when you look at the engine placement of the RCF, it is not any different. The weight distribution is the same 54/46 for the LSD and 53/47 for the TVD one. Shorter wheel base naturally responds faster so it will naturally have easier understeer/oversteer tendencies. Still, understeer is not something reserved for the RCF. The GSF has understeer as well. It is with TVD, you are able to get the rear end to rotate easily.
I drove both GSF and RCF TVD before I made my decision. Like I said, GSF felt big and much softer compared to the RCF, which is why I decided not go with my first option of getting GSF and went with the coupe despite not being a coupe guy. If I wanted more comfort and more space, I would have taken the GSF. The size is simply something you cannot mask. It is just physics. You are critical of the TVD, but is what makes the GSF handle much better than it should. All of the reviews give TVD the credit. There is a reason why Lexus never made an LSD GSF.
I have driven the 2016 - 2017 IS350 F-Sport extensively back in the day and the new IS350 is a modification of the same chassis. You seem very impressed with it, but C&D was not impressed with the handling calling the chassis 'flimsy' and saying even a Camry TRD had better handling than it.
Again, like I said before, RCF with TVD had a lateral grip of almost 1.00g. No Lexus this side of the LFA has accomplished it so far and until we see some actual numbers, those are just your biased claims.