I been reading some claims on the Red Sport..

That say it does high 12s bone stock.
But all the big magazines seems to have 13.0 listed one even 13.2

Also eveyrone seems ot agree that the stock dunlop run flast are heavy and have poor traction.
Could simply changing out the tires be responsible for a stock run in the high 12s?

Absolutely. Run flats are always junk, so it's highly likely. If a 13.0 is possible with run flats, then a better tire should make a high 12 possible.

Having driven both the RS and non-RS, the RS sure doesn't feel like a high 12 car in stock form though. I chock that up to the car just being lazy feeling in stock form. Upgrades can solve that fairly quick.

I switch to Mich Pilot Sport 4s and some Niche rims. Far better grip with the Michelins and noticeably quicker launches. My new Tire/Rim combo is also 9lbs lighter per wheel so the car is much more responsive with the reduced unsprung weight and more grip

245-40-19 factory wheel setup on my '17 RS AWD are 62lb each.

My new front 20x9 Forgestar F14's with 245's are 52lb and 20x10.5's running 285 are 56lb. Michelin PS4S

Yes, the runflats are stiff with crappy traction. They are easily popped and they tranline like crazy regardless of your alignment.