The F-35 and F-22 were designed for two totally different missions! The F-22 is a dedicated air dominance fighter with secondary air to ground attack role added later. The F-35 is a dedicated air to ground strike fighter. One is not a replacement for the other!
This makes absolutely no sense to me whatsoever. The F-22 is the worlds only 5th gen. fighter actually in service. Because of its first detection/ first shot, stealth, and extreme maneuverability capabilities, it requires fewer F-22s for an air supremacy mission than it does F-15s. It has common systems with the F-35, which helps keep its maintenance and repair costs down compared to the system we have now, where parts for the F-15 and F-16 aren't compatible with the F/A-18 Hornet and Super Hornet. So, despite it's $100 million price tag, which is inflated due to the constant reduction in orders for the jet, it actually makes more economic sense than the F-15! It's dominance over anything else in our and our allies' inventory was proven in actual head to head war games at Red Flag near Nellis AFB.
Regardless of which bird we use, we will have to have so many primary air superiority fighters in our inventory. Rather than continue to spend money on our existing fighters, why not replace with better technology that gives us "more bang for the buck" and does a better job at its intended purpose at the same time? The F-15 is a spectacular aircraft, with an unmatched air to air combat record, but as good as it is, technology has passed it by, and many of the existing F-15s in service are nearing the end of their airframe fatigue life, so they have to be replaced by something.
The F-35 is probably a great strike aircraft, and will probably work well for some other missions as well, but it was not optimized for air to air combat like the F-22 was.