OOA does come up way more than you think. For our Trojan War games, we've gone to Leaders/Sergeants who suffer an OOA wound roll by any model that isn't also a Leader/Sergeant instead treats it as 2 wounds.
That has come up a couple times, and makes a huge difference to gameplay (to the point it makes it more in line with the Illiad).
Glad you were able to have fun with your son, it's quite a joy to pass on a love for the hobby,