Not an expert and would defer to the folks here but perhaps the tangos used cheaply made clones of the AK, such as those made in Poland or China or maybe it was an export model. The training received by these people are typically far less than regular or even para military forces. How many rounds do they expend in training weekly/monthly? More likely a few times at most every few months clandestinely? The weapon is just one of the factors, training is another often overlooked attribute. The 7.62x39mm round does its fair share but as seen in the AK74 and later weapons by Izhmash, etc, other rounds were further developed with desired characteristics. AK has several factors going against it which was why further developments took place.
Sights, scopes etc on the rails are only supporting tools, nothing beats getting familiar with the weapon and being trained on the nuances and pitfalls. The furthest effective range set iron sights on the AK is way too far anyway but doesn't diminish its effectiveness. The quality of the rounds used is also another key factor as using the right rounds would make a difference in overall accuracy and performance. Not talking about match grade rounds, just rounds that have consistency in the production and have a low defective rate.
It probably would not have made much difference in this case given the close nature of the engagements which was point blank in some cases. I am a fan of the Galil family and would like to highlight that the 7.62x51mm nato chambering is not just for sniping. The long mag on the 7.62 mag makes it difficult to fire prone. Perhaps during the development of certain weapons such as the SCAR, some of its performance in the larger caliber would have been good for benchmarking. The search for the ultimate firearm goes on but i for one, if i would need to be handed a weapon by the SAF once more, would pick my trusty old one over something bullpup, it serves no real purpose even though so many countries like to develop it. I share what some folks feel about such weapons, serving a market that no one wants or needs. The M4 and deriatives like the HK416 are still being widely used. I guess i have digressed too much, leaving it to the exports to discuss.