I think you are looking at more of the set up as being difficult, but the infinite itself, it's really not that difficult at all. Even 3 hit pop up, forceball, one step in, and then infinite isn't really that hard, once you get the first hit of the combo, anywhere, you are in full control, and on Jax, Sindel or Sub, is easy as hell. There are even ways to mess it up and recover, but I would say netplay removes the chances of that specific concept in most cases, netplay itself is a reason why people don't pick Reptile much but that doesn't change the true mechanics. His inf vs the male ninjas, Kano, Kabal, female ninjas, etc, very difficult.