Let's try a sorcerer army, just for fun:

The Front Line - 300 Half-Orc Stone Sorcerers
Cantrips: Booming Blade, Green-Flame Blade
Spells: Thunderous Smite, Wrathful Smite [From the Metal Magic feature]
Equipment: Since Sorcerers only start with simple weapons from their starting equipment, let's give them all Spears, which they will wield in two hands for 1d8+Str. Stone Sorcerer grants proficiency in simple weapons, so great.
Notes: With the smite spells, the Front Line should be able to cause confusion in the front ranks, assuming a reasonable portion of opponents fail their saves. With Half-Orc and Stone Sorcerer abilities combined, the Front Line should be able to hold out for marginally longer than your average sorcerer.

The Phoenix Corps - 200 Tiefling Phoenix Sorcerers
Cantrips: Firebolt, Gust, Thaumaturgy [From Tiefling]
Spells: Burning Hands, Chaos Bolt
Equipment: No special notes here, just your arcane focus and a loaded crossbow.
Notes: Hanging back behind the Front Line, the Phoenix Corps blast their opponents with Chaos Bolts and Phoenix-boosted Firebolts, and enemies that get too close are pushed back by gust and torched with Burning Hands.

The Divine Bastards - 300 Protector Aasimar Divine Soul Sorcerers
Cantrips: Firebolt, Mind Sliver, Light [From Aasimar]
Spells: Sleep, Shield, Cure Wounds [From Divine Soul]
Equipment: Again, no special notes.
Notes: Begin the battle by Mind Sliver-ing the enemy ranks, allowing the Front Lines to hopefully crash through, and continue the battle as medics or as a last-ditch effort against flying forces (Sleep on flying enemies would be interesting).

The Controllers - 150 Half-Elf Stone Giant Soul Sorcerers
Cantrips: Mold Earth, Frostbite, Resistance [From Mark of the Ordning]
Spells: Fog Cloud, Catapult, Entangle [From Mark of the Ordning]
Equipment: See above.
Notes: The Controllers seek to cause as much trouble for the enemy as possible, by Entangling the charging soldiers, Fog Clouding the ranged units, and Frostbiting the currently engaged ranks.

The Shadow Hand - 50 Changeling Shadow Sorcerers
Cantrips: Message, Poison Spray
Spells: Disguise Self, Comprehend Languages
Notes: The Shadow Hand are this armies spies and information-gatherers, using their unique abilities to pose as a member of an enemy camp if possible.


I really hope UA is allowed or this was all a waste of time.