I'm going to go out on a limb here, and say the argentines were lucky to do as well as they did.
The navy had no answer to ssn, and it was only because the British pulled their punches that they didn't suffer worse. Conqueror could have easily sunk belgranos 2 escorts as well, and there were 2 possibly 3 chances to sink their carrier too, which wouldn't were missed because of political reasons (waiting for the Peruvian peace plan, just inside 12 mile limit, etc.), whoch wouldnt have been missed had the shoe been on the other foot. That basically means the Falklands garrison is bottled up, a giant self imposed pow camp.
The argentine army was totally outclassed. There is a good argument that 3 commando brigade could have done it better for the British by themselves and with less casualties. British commanders seem to have thought so - there is a lot of criticism of having to wait for 5 brigade, of 5 brigade not being combat ready, at least some of it seemingly valid (bluff cove happened, in part to save 5 brigade walking). Think about that for a minute. If 3 brigade had done it by themselves think about the troop ratio... We're in 19th century colonial war territory.
That leaves it to the airforce/FAA to sink the landing force or carriers.
We can talk about bomb fuses, but however brave their pilots, their technical and maintenance standard was poor - not working ejector seats, inability to repair them, inability to repair inflight refuelling equipment, they didnt actually have the manual for the bombs or fuses (and nobody thought to get it before the war), etc.
Not extending the runway is typical of that kind of thing, not an unexplainable oversight,. Moreover argentine military engineering of all types, including combat engineering was poor (think about how they failed to properly use potential natural fortresses to protect Stanley). In fact, all the support elements of the argentine military were poor (not macho) - they left their troops for weeks in wet hills, didnt feed or supply them properly, didn't rotate or rest them (or give them a chance to dry out), and the officer's response when troops were unhappy was to stake out (or in a few cases shoot), a few malcontents at random.
And even of they did extend the runway, so what? The whole area around the airfield was peppered by British bombs (from harriers as well as black buck), and naval gunfire. Not a great place to park aircraft, spares, fuel, or bombs, especially with no hardened shelters. And how do these items get to Stanley, do they fly them in?
And let's suppose their airforce does better. So what?
Can they realistically stop the landing? Seems unlikely to me - best case seems to inflict more casualties.
What about sink a carrier? Again seems unlikely given the relatively large size damage control, etc even if they score exocet, torpedo, or bomb hits. A mission kill maybe. British answer is to keep fighting - illustrious is on the way, and they had already planned for a possible "stone aircraft carrier" - to build a base for buccs and phantoms, - moreover some of the gloves probably come off, which is not good for argentina - naval shipping in the 12 mile limit gets sunk, phoenix squadron is history, etc.
And don't forget the British had their share of bad luck too - rapier problems with salt water exposure, Atlantic conveyor getting hit before it could offload the helicopters, John Nott as defence secretary, etc., - but they were able to overcome these obstacles.
(of course none of this was obvious at the time, or even soon after)
