I think its important to note that I (and I assume Teridax too) don't want to remove the guardian from Battlecry and make it an archetype instead, but rather say that the class could be an archetype because we want the class to gain an unique flavor and mechanics that make it stand on its own.

Guardian fills a similar niche to fighters in that a fighter "fights, while the guardian "guards". if that's the case and what the devs intended when making the guardian, then I think taking the fighter's chassis but reversing it is IMO the first step here.

Fighters start being experts in weapons? Then guardians should with armor.

Fighters start being trained in advanced weapons? Well, there aren't advanced armors or anything like that, but receiving armor specialization benefits at 1st level can do the trick.

Fighters have Reactive Strike? Guardians have Intercept Strike.

Taunt and Threat Technique don't need an equivalent.

Bravery would roughly be the equivalent of Tough To Kill.

Fighter Weapon Mastery → Guardian's Armor Mastery

Weapon Legend → Legendary Armor

Otherwise, a guardian would still have an average martial progression (expert with weapons at 5th level, master with weapons at 13th level, weapon specialization at 7th level, greater weapon specialization at 15th level). I feel this is the most basic chassis from where start to build up stuff for the guardian to become more unique.