There's a lot to like here; name is good, ability meshes.

But I still kinda hate it. It feels like it's missing something.

What if it had Flash? Too powerful?

I can't think of a good reason to give this Flash or Feint, as neither ability would allow you to use the ability that defines its medical affiliation.

The only slight shift I can think would be to separate the damage-prevention into two abilities that might reinforce the concept of "triage". Something like:

T: Prevent 1 damage to target creature or player. T: Prevent 2 damage to target defending creature.

But that doesn't do enough in terms of gameplay that I would really ever make that change. Plus, clutters the rules text.

Well, while a touch of a stretch, triage originating as a way to help soldiers on the front lines could suggest 'medical help in a hurry', thus my suggestion of Flash.

I read him as "overworked medic capable of patching up multiple dudes in a high-action scenario".

His Untap trigger was all wrong; the "spells during combat" thing is a "media" theme here. The Medic is not media.

I like the reworded trigger but three mana is a lot for it. At uncommon, should it come down one? Or is it too combo-lish at 2?

Dan, I'm surprised! You're the hater of all things un-fun, and dealing with an army of piss-ants that just won't die is definitely un-fun. Three mana keeps him saving two, maybe three points of damage per transaction at most and ties up your resources that would otherwise be putting more piss-ants on the table. It's a number that strikes a balance point.

I'd actually recommend that you revert it back to the earlier trigger for two reasons:

1. Your reasoning for changing it is almost too high-concept. While it's good for you to use the story and conceptual details to guide your design process, I don't think it's vital that you maintain absolute adherence to such rules, especially if they lead you to creating an ability that is basically the same thing but (ironically) less flavorful.

2. Of the White creatures that possess activated abilities and can untap, all but Barrenton Medic respond to the casting of spells.

It's also awkward if you were to have this AND Dispatch Field Reporter in the same set, in that they explicitly represent a pair that was then separated.

I dunno: I just don't see four mana as being that much different than 6 mana in combat situations. That's still a lot of mana to withold in order to prevent two damage. But I certainly get that it may be too aggressive.