No, it was designed to kill tanks, not personnel. Its 30mm cannon is complete overkill for that role.
Apaches are MUCH better for ECAS, and GPS guided bombs are fine for the general CAS role (with troops cuing the targets by laser cartography).
Essentially, a prime mission objective is to loiter over an area and provide air support. Something most fast-moving aircraft are not exactly made to do. If a request comes in to target a tank; the plane kills the tank. If a request comes in to target a truck; the plane shreds the truck, and whatever happens to be inside, to shreds. If a request comes in to strafe a defensive position; then the plane puts big holes in those defenses. As for personnel, the plane may not kill them but it sure as heck puts a good scare into them. Stories indicate friendly soldiers like seeing, and hearing, the plane in the area during a firefight. It has more uses than the bullets it fires.
Also, keep in mind that the A-10 can carry other weapons than just the cannon it's built around.
Now, is it expensive in today's world for that purpose? Probably so.
Apaches are nice too. I'm sure one day someone will consider them an expensive disaster as well.
Give it the wrong job and, sure, it will fail.
What the last decade plus had demonstrated, is that there is still plenty of work around at which it excels. And for which the military as yet has no comparable nor superior replacement.
Ongoing, critical work (well, if you insist on being in that theater, to begin with).
In the middle of building a house, you don't throw out your existing hammer two weeks before the new, improved model with the carbon nanotube handle maybe becomes available.
Developers aren't ditching their monitors because in 1 - 3 years maybe Oculus and the like are going to give us "infinite", 3D viewspace.
I'm sorry to get a bit emotional and strident, here. But a problem the U.S. military has, is -- in good part, for politics, personal power, and money -- bypassing more effective and economical systems for marketing that has yet to be substantiated. They have enough raw resources and innovation to eventually brute force and trick around the resulting limitations, but it costs a lot -- including sometimes lives.
Nobody is suggesting the use of a decades-old aircraft against a modern air power. But when you already have air superiority, it is better to use dedicated aircraft like the Super Tucano, as you mentioned.
My emphasis is not to bring back the A-10, but to remember the effectiveness of that style of fighter and why it has a place on the modern battlefield, especially when the enemy is in inaccessible terrain and they lack the resources to achieve air superiority.
Those are nuclear powers. The only possibilities of F-35s shooting at Chinese or Russian jets is "accidents" like the Turkish border incident. In the event of actual war they'll be destroyed on the ground by ICBMs, along with everything and everyone else.
[1] http://dodbuzz.com/2015/03/06/afghan-military-to-receive-its...