The US is still flying F-16s, F-15s, F-18s, and F-22s. They have hardly been phased out (they are actually being upgraded). The F-18 is still in production, and it is made by Boeing, not LM. It would be a total loss for LM if the DoD went with any legacy fighters except the F-22.
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The F-18 is the wrong choice for the USAF. F-15SEs would make some sense, but they would need developed further.
The F-35 is in the air, in about the same numbers as the F-22.
Lockheed doesnt have a monopoly, Boeing is still making F-18s.