Why does the Navy want 22 more Growlers when they have all those F-35Cs coming on line (we hope) soon? It's all about the electronic warfare:
The F-35 is targeted against a narrower array of frequencies and emits only in a fairly narrow swath in front of the aircraft, according to Manazir. (The F-35 is the only US aircraft designed to defeat the most advanced Russian anti-aircraft systems such as the S-400 so the guess is that the JSF emits in frequencies designed to confuse and disable the radar systems that feed those.) The Growler can engage in electronic warfare not only as it flies forward but continues to emit even after it begins to return to base. I asked Manazir whether the F-18′s lack of stealth meant the Growler would have to fly separately and far behind the stealthy F-35, but he said the Growler generates enough power to blanket the area ahead of the F-35s so they can act in a complementary fashion.
I believe it was Mr. Lion saying here in the comments the other day something about more airframes being better -- and it's nice to have a healthy variety, too.