- The A-10's survivability is overrated. The Air Force conducted studies after both Gulf Wars and found that the A-10 was taking higher damage per sortie when compared in '91 to '03. That Iraq's air defense was in shambles didn't seem to diminish the fact that the A-10 was becoming more vulnerable to more sophisticated weapons. Technology has made cheaper weapons more effective since the 1970s in which this was designed. In a higher threat environment, the lack of sophisticated sensors, threat identification, and ECM is seen as not boding well.
- The A-29 is a fantastic plane. But it's giving the A-10 a run for it's money, not the F-35. In the low-threat COIN environment, it has all of the benefits of the A-10 with none of the drawbacks. That famous cannon isn't always idea against militants in the mountains when you're worried about spraying your own troops. That the A-19 can carry small guided weapons just like the A-10 gives it capabilities where it counts. And it's half to a third of the price to purchase and maintain.
So the A-10 is getting squashed from two sides: The F-35 can penetrate the high-threat environment, and provide CAS in a lethal SAM environment, while the A-29 can provide CAS/COIN against militants in a low to non-existent threat environment. There is no middle ground. It left when air defense systems gained the sophisticated tracking and accuracy that wasn't there in the 1970s and 80s.
The A-10 was a fantastic plane and well designed for the time in which it was envisioned to fight. But even I agree that it's time has passed. Like the F-14, it's sad to see it go, but I think it's the right call.