No one uses Comfort tires in D1 or Formula D. I've attended both completions and walked the Pits. Most use shaved Falken Azenis tires or some Equivalent.
They may not use comfort tyres in the real world. But this is GT5 and the comfort tyres are the closest selection of tyres compared to the real world. Sure they are still very different but much closer than sports and much much closer than racing tyres. With comfort tyres you can hold a nice, smooth slide that is very consistent. Sports on the other hand are very in-consistent tyres meaning you can't get slide after slide of smooth drifting at a reasonably realistic drifting speed.