[T]he Navy and Air Force are already courting concepts from the defense industry on separate sixth-generation successors to the F-35, called the FA-XX and Penetrating Counter Air respectively.After the frustrations experienced in reconciling the Air Force’s and Navy’s differing demands for the F-35—and the mere 20 percent parts commonality that resulted between the two—the two services have little desire to jointly develop the Lightning’s successors. The PCA is intended to be a long-range escort fighter that can accompany forthcoming B-21 Raider stealth bombers into enemy airspace and protect them from enemy fighters. The FA-XX will likely be an interceptor that can better protect Navy carriers from enemy bombers and missiles.
And why are we buying the F-15EX (an upgraded fourth generation fighters) again?
As simple as just building new F-22s may sound, the truth is, re-starting the F-22 production line would likely cost the same or potentially even more than simply developing an entirely new and potentially better fighter. Lockheed Martin cannibalized a great deal of the F-22’s production infrastructure to support the ongoing production of the F-35, meaning it wouldn’t be as simple as just re-opening the plants that had previously built Raptors. . . .Boeing’s new F-15s are considered fourth-generation fighters that are sorely lacking in stealth when compared to advanced fighters like the F-22 and F-35, but the Air Force has agreed to purchase new F-15s at a per-unit price that even exceeds new F-35 orders. Why?
There are a number of reasons, but chief among them are operational costs (the F-15 is far cheaper per flight hour than either the F-35 or the F-22), and immediate production capability. Boeing has already been building advanced F-15s for American allies in nations like Qatar and Saudi Arabia, so standing up a new production line for the United States comes with relatively little cost.
The F-22’s production line, on the other hand, hasn’t existed in nearly a decade. In a report submitted to Congress in 2017, it was estimated that restarting F-22 production would cost the United States $50 billion just to procure 194 more fighters. That breaks down to between $206 and $216 million per fighter, as compared to the F-35’s current price of around $80 million per airframe and the F-15EX’s per-unit price of approximately $88 million.
UPDATE (July 1, 2021):
Meanwhile, the military of Switzerland has agreed to buy 36 F-35A fighters (Lockheed) for $6.5 billion, after having decisively defeated the bids from Eurofighter Typhoon (Italy’s Leonardo, the U.K.’s BAE Systems, and Airbus), the Dassault Rafale, and Boeing’s F/A-18E/F Super Hornet. Lockheed's F-35A bid was $2.16 billion cheaper over 30 years than the next lowest bid, and also outperformed its competitors for the contract in all respects in terms of performance measures:
[T]he F-35 scored better in effectiveness, product support and cooperation than the Rafale, Super Hornet and Typhoon. The Federal Council pointed specifically to the Joint Strike Fighter’s survivability and situational awareness as selling points that were seen as advantageous for the Swiss Air Force’s air-policing mission.“In terms of effectiveness, the F-35A achieved the best result because ... it includes entirely new, extremely powerful and comprehensively networked systems for protecting and monitoring airspace,” the Federal Council stated.