Wrong the Stinger and Igla has a limited distance 6,000 m (20,000 ft) for Igla and 4,500–4,800 m (14,800–15,700 ft) for Stinger.
Also the artillery has more range than any Stinger or Igla, and perhaps I explained bad but you pave a road with bomb for the Helix to pass over it ensuring that no one is there with a RPG or AAA, also if you know were is your troops you know were to shot at and when to stop, and after you get to the place for the medivac the artillery fires in barrier around the elzy to avoid enemy troops for getting in the zone.
And yes you can do this if the medivac is in range of the artillery, if not you have to use another tactic.
Shinigami Out...