The F-16 is the "low" part of the "high/low" multirole fighter strategy. For the air force, the "high" jet is the F-15. The F-22 is predominantly designed for air superiority, and thus is most directly a replacement for the F-15C. Whether it really even replaces the F-15C is questionable, since the quantity produced is extremely small compared to the overall legacy fighter fleet.
The assumption is that gap will be filled by the F-35 and the F-16 will be replaced by the F-35.
Nope. F-16 and F-18 are of comparable class, F-18 being built for Navy requirements and F-16 for Air Force. IIRC they even evolved from a common program at one point. They separated as Navy and AF do not mix well, as is demonstrated by the JSF program.
