But it’s beyond time for this meme to die.
The A-10C just isn’t suitable for this task any more. Low and slow just doesn’t cut it. It’s slow to respond due to a cruise speed of 200-220KIAS (compared to 550-575KIAS for an F-15E). Having to get to within 1.0–1.2nm to employ the famed GAU-8/A Avenger (or rockets) makes it a MANPAD and AAA magnet. The gun is limited in the types of targets it’s effective against nowadays as well. And if you aren’t using the gun or rockets, you’re dropping JDAMs (GPS and laser-guided bombs) or firing air-to-ground missiles like Mavericks. If you’re using these, you’d rather do so high and fast: you get both increased effective range and more forgiving margins of error during weapon release.
And if you’re doing this, you might as well just put them on an F-15E which outclasses the A-10C in terms of carrying capacity, response time, survivability (unsurprisingly, not getting hit because you’re at 600KIAS at 30,000ft is better than surviving being hit because you were flying 250KIAS at 500ft), weapons availability, and virtually any other trait you can imagine other than “loiter time”.
And response time trumps loiter time hands-down, especially when loitering dramatically increases the odds of losing the pilot and/or airframe to surface fire. On top of this, if you're in permissive airspace there's always a tanker nearby to extend your ability to loiter (and if you're not in permissive airspace, your A-10C fleet is grounded anyway).
The A-10C is lauded, and rightfully so, because it was such an effective CAS platform. But it’s not any more. All of the praise you hear about it it real and deserved, but comes from the perspective of people who saw it in action because that’s the plane that filled the role and so that’s the plane they saw in action. With other planes now filling that role, you will hear the similar praise about those planes for pretty much the same reason. The people who aren’t singing its praises are the commanders who see the frightening number of lost or damaged airframes and see how poorly it stacks up against other planes readily available in our fleet.
Edit: And I have to respond to this point.
> We know it's a hell of a lot less reliable than existing US aircraft and competing foreign aircraft.
The F-35 is literally one of the most reliable aircraft we have ever flown (second only to the F-22). Since 2006 (thirteen years), we've had four losses. For the F-22, it's four losses in twenty-two years. The F-15? 46 were lost from 1972–1985. And nearly twenty-five percent of our F-14 fleet has been lost in non-combat accidents.