So the healing wings are supposed to be the Weyrn of supporters and medics on the field.
The Obsidian Warders are the first line of defense that gets send in first like a vanguard of the army.
The Dark Talons are the secret weapon aka a elite force held back until the enemy is broken and then attacks to target the leaders directly.
What are the jobs of the other two factions? Did they explain what the troops of Emberthal did do as part of the grander forces for Neltharion?