Warfare in Trek is a very plot affecting thing. Realistically, you'd think you can do stuff like use your ship in orbit to give you aid. But then things like the plot of AR-558 had it that the Defiant had to leave orbit and deal with Jem hadar fighters, which also conveniently left orbit as to not give the Jem Hadar an unfair advantage.
In general, I can't recall any eps (TNG and beyond) that really had ships supporting groundside battles, they always were 'somewhere else' or 'happened to get blown up' or 'there's a big shield around the planet'.
Lets assume for example a ship happens to be in orbit in support, and no plot preventions to inhibit them to fire down on the planet in support. Then we'd move on to more internal prohibitions.
Mechanically, per the game system, stun affects all types of the same species equally. Sickly old dude gets stunned for just as long on the same setting as healthy young dude, or baby in cradle..dude... If you looked at it more, its easy to see this is more for ease of game mechanics than what would be 'realistic'. You shoot a baby or preschooler with phaser setting 1, and it should probably be more dangerous than shooting uppity adult dude with the same setting.
Fed types at least would probably worry about collateral damage from something like 'stun the city block' since there'd be too many variables in people to worry about. What if our stun setting kills kids, or drops the dude with the 24th century pacemaker? Sure evil dudes or Klingons wouldn't care, but they probably wouldn't use stun in the first place. Fed types would worry about and be considerate of such possibilities.