A helicopter on the ground is dead meat.
None of these fights are likely to lose, unless the modern unit is damaged.
Damaged modern units are low on repairs, ammunition, armor and fuel. Just because the unit is "maceman", doesn't mean that maceman cannot raid an insufficently defended supply base, steal bottles and fuel, then use them against you.
Against a well-equipped army, this isn't much of a danger. But when your force has been beaten down by a huge low-tech army attacking it, some of their troops are going to get through the lines and steal some supplies, and your out-of-ammo, low-on-fuel, out-of-food helicopter assault force is having a nap with insufficient guards, a "maceman" using stolen equipment can throw a cocktail onto your fuel tank, and ... there goes your helicopter unit.
If you look at the odds that a helicopter or a modern tank has against a primitive unit when undamaged, they are pretty ridiculously biased in favour of the modern unit.