Gerrey got a few things wrong here.

The Emplaced Anti-Tank Cannon (EAT) is manned by a player and has 45 meters max range. It has much greater health and will stop tank pushes or be a serious hinderance, only fools will lose their tank against a well placed one(unless they decide to rush it).

The Anti-Tank Garrison is a bunker upgrade that does AT turret damage (whatever that is) and has a firing arc of 150, and an engagement range based on the visibility at the time like normal AI defenses. It also returns fire when hit no matter the visibility up to ~50 meters. Similar to the normal AT turret like how the Rifle Garrison is similar to the foxhole.

They are functionally entirely different structures, so cost and stats or whatnot don't matter. If you have them incorporate AT garrisons into your bunker defenses. EAT is good for pre-planned positions and mostly frontlines, and more often used since most bases don't have AT garrisons unlocked.