The way it's made requires a lot of dedication -> gathering everyone, organisation to communicate can be tricky particularly if you want realistic kind of comms: teamspeak is still required (I don't think there's a realistic mod for Arma 3 compatible with Discord).
Nevertheless, Arma 3 has everything you need:
Big maps (open world)
An actual map (I am talking about the paper/GPS thing) -> with actual elevation information on it, etc.
Complex strategies and tactics possibilities
Communications
Vehicles: helicopters, tanks, cars, trucks, planes, boats, etc. etc.
A very WIDE set of weapons of all kinds: turrets, firearms, launchers, mortars, etc. etc.
All this adds up to the need of coordination, planning, preparing strategies, primary objectives, secondary objectives, backup plans, backup plans for your backup plans, etc.