During the 1960's the primary mobile air defense missile of the US army was a variant of the AIM-9 Sidewinder mounted on 2.5 tone trucks or tracked APCs. North Vietnam fielded something similar.
And the USSR already have "Krug" (SA-4), "Kub" (SA-6) and "Neva" (SA-3) by the end of 1960th. The level of battlefield anti-air defense, achieved by the soviet divisions in 1970-1980 made the chances to A-10 survival... slim.
The A-10, like every other aircraft except the F-117 and B2 Spirit, benefits from having air-superiority top-cover, but it doesn't really need close escort; it flies too low and too slow for fast fighters to stay with it.
So, without the aerial superiority it would be really hard to not get you A-10 slauthered by the enemy fighters.
The A-10 does have several AA "Kills" to it's credit; it isn't completely helpless.
Yes. Against helicopters and light planes.
The IL-76 ("Candid") heavy cargo plane also have rear gun turret, and theoretically could shot down helicopter or some light plane. Doest it means that it could operate without heavy escort against enemy fighters?
Yes, the A-10 have SOME ability for air-to-air combat. But only some. Against something like modern fighter, he is completely defenseless, and even old supersonic jets like F-4 or Mig-23 could easly bring him down, just because they are a lot faster, have better suited anti-aircraft fire control and anti-air missiles.
The F-15E Strike Eagle is very accurate with smart munitions -- at a million dollars or so per shot.
Really?
The good old JDAM cost only about 25000 per unit, the SDB - from 40000 to 250000 and only JASSM-ER - with her 1000-km range - go over the million.
Compare that with the cost of A-10, and?...
The A-10 OTOH, carries a mix of smart (LGB and AGM-65 Maverick) weapons and small dumb bombs (250 lb GP or 500 lb GP) or anti-personnel cluster bombs. It can deliver those "dumb bombs" with very near the accuracy of the smart weapons. A-10s deliver ordinance in hundred dollars to thousand dollar increments and can hang around a lot longer than faster multi-role Aircraft.
Yes, against outdated air defense for some third-rate nations.
The air defense of first, or even second-class world nations simply would not allow the A-10 to "deliver those "dumb bombs" with very near the accuracy ". The anti-air missiles and autocannons also go forward, and with advent of active-seeking SAM, the detected A-10 simply would not be able to survive long enough.