I've been looking at the Tactician Archetype for the Fighter and I'm wondering if using the Cooperative Combatant ability with the Covering Fire Feat.
If the attack is successful, that ally gains a +2 bonus to AC against that opponent’s next attack, as long as the attack comes before the beginning of your next turn. All allies with this feat also gain this bonus against that opponent.
Basically, I pick a single ally, even if they don't share the same feat, and I can aid another them to increase AC. Sharing the same teamwork feat is just an additional bonus.
So, if I am reading both of these right, with Covering Fire I can do a ranged aid another which aids multiple allies instead of just the one who doesn't have the feat, almost getting around the entire need for the Teamwork part of the feat then? Also, since Covering Fire says that its only AC that is increased, while Cooperative Combatant says I pick either, am I correct to assume that I would only increase the AC of my allies since the Covering Fire part is explicitly saying that it only increases AC?
Covering Fire allows you to use the aid another action with a ranged attack.
Cooperative Combatant allows you to affect additional allies with the aid another action.
From a balance perspective, Covering Fire can theoretically be granted to all allies by a Cavalier's Tactician ability as well from level 1. There's nothing overpowered about the Tactician Fighter's level 11 ability duplicating this.
You are correct that you should only grant +2 AC with aid another when doing so as a ranged attack. You couldn't aid another on attack rolls using Covering Fire, or other typical uses of aid another such as skill checks or saving throws.