The Atar 9K will have only support from SNECMA until 2020, perhaps a little more, but not far from 2025. It's only postpone the problem until that date. The Mirage 2000 is by far a better choice.
I'm sorry, but you can't measure the fighter's performance only by its combat reports, remember than any air combat is never equal to the next or previous, and every conflict have its unique circunstances, the aircraft performance can be affected by an arms embargo, lack of trained pilots. lack of spares, poor tactics and strategy, etc... In Malvinas by example, the Mirage IIIEA was unable to exploit its superior performance against the Sea Harrier because it lacks of an In-Flight Refuelling Probe to have the sufficient fuel to employ its full capabilities. And so on...
I don't think than obtain the Su-27/30 can be impossible for the FAA; as I mentioned before, exists a batch of second-hand Su-30s in KnAAPo than you can request at a fraction of a cost of a brand-new fighter, also Ukraine and Russia have a large stock of Su-27 stored as reserve than you can request for overhaul and purchase. This must be followed with an comprehensive upgrade for the A-4AR as a complement for the new Flanker fleet. If countries like Ethiopia and Eritrea can buy Flankers, why Argentina cannot?
Greetings from Perú.