up to 1998 Targa cars ran on street tyres, and back then it wasn't as restriced so the cars had more power than they do now. And they seemed to hold up fine back then.
R tyres are shit house in the wet. Fern Glade in Targa this year was like an ice skating ring, tyres were bone cold at the start, and still bone cold at the end.
Having said that, I don't realy want to see R tyres go. But compared to some of the other slowing down options (speed limits, heavier car restrictions) it's not such a bad option.