Not All A-4s Were The Same!!
The A-4M had a P408 engine which was much more powerful than the P6 or P8 which powered earlier models. Different as chalk and cheese.
Plus, the SeaJets and Argentinian A-4s were flying very different missions, and were armed in very different ways, so comparing SeaJet air-to-air success over early model A-4s in an air-to-ground fit in that conflict is not a good comparison.
In peacetime training, an AIM-9L equipped A-4M and and AIM-9L equipped AV-8A were a good match, with the winner usually the better air combat pilot of the two.
So declaring all A-4s to be toast against Sea Harriers is somewhat misleading - IMHO.