You cannot continue to go out and fight with older weapons though.
Nominally, the F-15/F-16/F-18 are not as survivable in a modern air war.
The F-35 is a compromise design.
Mostly it compromises its ability to loiter on the target, carry large amounts of munitions, and dogfight.
So as long as you don't want to do any of those things, the F-35 is better than older weapons.
A proven fighter is one that has been through the teething problems that the F-35 is going through now.
Ha! The F-35's issues are not "teething problems," they are R&D problems.
The F-35 is a procurement disaster of such epic proportions that tomes will be written to warn future generations on what not to do.
Just to stay on topic, one of those tomes will talk about engine problems and why the military should source 2 different engine designs.
It will also mention that, because of the F-35's unprecedented budget overruns, the second design was canceled.