Simple. If china already has fighter that can challenge F15, F16 & F18, what left behind is F22/A, and CHina has no confidence of SU35 to beat F22/A unless Russia can transfer the total know-how of SU35 or otherwise it makes no sense for buying an inferior fighter to F22/A already. This is the matter of cost effectiveness in air-space competition. Instead, Russia may have to consider to buy China J14, J15 etc for the year to come to protect their air space.....China and Russia can only be friend to each other and hence we believed that China has no hesitate to shall J14, J15 later on to his friend such as Russia, Pakistan, North Korea, Burma etc...