Well, the F-15 and F-16 are staying on for many years to come for a reason. It's not just the much higher costs of the F-35. How they might be used is to go ahead of the F-15's, strike some targets and identify for the F-15s where they can bring their much heavier load to bear. Even with pylons used, it has a lower payload than the F-15, and is ludicrously too expensive to do the A-10 missions. In low threat environments, you dont use a fully loaded F-35, you use a turboprop like the A-29 or AT-6 Wolverine or you use the A-10. Ive seen the F-35 rated as slightly superior to the F-16V or Gripen-E in air to air combat. But is blown away by the F-22. Adding too many roles makes it hard for it to be the best at anything. One area is situational awareness. Amazing information networking gives unprecedented awareness for the pilot. It is almost certainly No 1 in the world in that area. Networked with legacy platforms is certainly a useful role, but we paid an historically ginormous sum for that. And to beat systems like the S-400 that might not be nearly so fierce as advertised.