I was on CX403 TPE-HKG yesterday. It was a 77D, and I was seated in business class 2D. It was clearly a 3-class flight sold as 2. To all practical purpose, the service was as good as F except that they offered only business class breakfast.

F is probably not important for short routes like PVG and TPE. Having said that, there is still a huge difference between the F & J cabins even for 3-class sold as 2. With 2 dedicated SPs (and the curtain between the cabins closed during flight), it is very relaxed and the SPs are very attentive in the F cabin. The main J cabin is too large and service is often in a rush.