- Beyond Visual range air-air against a peer
If the mission is beyond visual range air-air combat with a new airframe (J-20/Su-35/etc) then the F-15X is not as good as an F-35. The F-35's stealth will allow it to hit the enemy before it's even detected. And against something like a J-20 or a Su-57, an F-15 is outclassed but an F-35 can compete.
- Within Visual range air-air
Why are you dogfighting in 2030? But if you are, three F-16s are better than two F-15Xs, at the same or lower cost.
- Combat Air Patrol
If the mission is long term combat air patrol (like enforcing no-fly zones against Serbia or the former Iraqi government) then three F-16s do better than two F-15s, at similar or lower cost.
- Close Air support
If the mission is close air support, then a pair of F-15s is not as good as eight Apaches, six A-10s, or three F-16s. The F-16s and Apaches are available as new-builds, and the A-10s just got re-winged.
- Deep penetrating strike
If the mission is deep strike against a serious air defense system, then the F-35 is a better answer. There are conditions that will kill an F-15X, but allow an F-35 to continue the mission.
Seriously, for which mission is the F-15X a better, more economical solution than the same money spent on a different platform?
Note: Most of the charts have an F-15 operating cost closer to 3x that of an F-16. The 1.5X used here is a kindness.
https://www.forbes.com/sites/niallmccar ... ead701685f