Sure You have a good point here. Also the turbos of that time suffered from very notable lags and the turbo RWD cars were considered very difficult to drive.
I guess You might be interested in a fact that even here in the East we had some turbo cars in 1970' though none of them made it to rally homologation (mainly due to socialistic politics of the state which didn't allow making "expensive" road cars and therefore also suitable turbos in large scale).
Here is one - Škoda 2000 MI used on circuits and hill climbs since 1975. It wasn't very successful due to low reliability. If I understood right they had problems with the wastegate etc.
http://www.skodateam.cz/Skoda_2000_M...-img_02wwk.jpg
http://www.skodateam.cz/Skoda_2000_M...-img_02xsY.jpg
http://www.skodateam.cz/Skoda_2000_M...-img_02y4w.jpg
http://www.foltyn.cz/car/skoda/s2000mi_5v.jpg
The engine was 2.0 litre OHC I4 from Škoda which was never allowed into production (actually same engine as used in quite rare rally cars Škoda 200RS and 180RS). The capacity was reduced to 1.77 (87x74.5) to keep the car in 2.5 litre class. The compression ratio was 6.8. The turbocharger was KKK with wastegate but without intercooler. The engine had single throttle valve and indirect fuel injection into four air channels just before the cylinder head. It used Schafer fuel pump. The power was 238 Hp at 6000 rpm. Compared to 130 RS here the engine was in front of the rear axle and it was therefore mid-engine car.