I don't dispute there will be more than one drug that is widely used in HCV.
Let's look at the world say 10 years from now - that pretty much restricts the universe of drugs to those that are already in the clinic or late-stage preclinical. So how many HCV drugs will have substantial (>$500m) sales? I'd guess less than half-a-dozen - perhaps only three or four. (But HCV is really not my space, so I will defer on this to the experts here).
In contrast, how many new oncology drugs will have substantial sales 10 years from now? I'd guess maybe 20, and if you look out further, that number will grow. And "substantial" here might well be multi-billion.