So the total amount of OPFOR KIAs would be...
2 Frogfoot pilots + 2 Hind pilots + 1 Albatros pilot + 21 MBT crewmen + 15 BMP crewmen + 6 BTR crewmen + 3 Shilka crewmen ~700 Garrisoned Infantry (1 battalion) + ~350 Special Forces/Recon Infantry (2 companies) + ~1400 Motorized Infantry (2 battalions) + 6 Mortar gunners = around 2506 OPFOR KIAs.
Unless ArmA 3 counts their unit sizes differently or my knowledge is incorrect, that is just a ridiculous number.
Keep in mind there were two enemy forces battling each other throughout the mission, we just inserted ourselves into the middle of it and made sure we came out on top. 
Not to mention that to a certain extent, you have to consider firefights in ARMA don't necessarily go the way they do in real life, and that its also Zeus's job to ensure that
everybody is participating. That means making sure every Private on the ground sees something of the engagement, every squad leader has to maneuver and coordinate, that the platoon leader has to always be watching the whole of the field to coordinate his squads, that Havoc 4 doesn't just bring along the tubes for nothing, and that Warlord and Thunder aren't just uselessly fluttering about overhead with nothing to do for most of the operation.
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