Spies will spy, but no spy makes the sort of money needed to produce a modern plane from scratch, and Israel cannot afford to either - they are having some major financial problems at the moment.
An F-16 may or may not be a match for either the MiG-31 or SU-30 series. The Lavi certainly was not. There is only one operational 5th gen fighter - the F-22 (and possibly a Chinese knock off in testing) - the F-22 is not exportable thanks to the (ex-Dem Senator) Obie Amendment. The current state of the tooling is unclear.
Umm, the Lavi would have arguably been a better match against the Flanker variants given its design, though the engine would probably need a boost, over time.
Why do you think the Europeans adopted the delta-canard configuration on all the fighters they developed in response to the Flanker?