Every single army you encounter in Quick Battles is comprised 75% of either cavalry or flying units and a lord on a flying mount.
The player then proceeds to exploit flying/cavalry unit movement mechanics to assassinate all damage dealing units regardless of how many anti-large or other infantry units are near them.
However, this isn't about winning or losing against such armies. The problem is different.
The Problem: This is not Total War.
Total War is a game about stereotypical armies (mostly infantry) clashing in epic battle across various locales. The battles in Total War are meant to progress at a measured pace and allow players to make tactical decisions based on circumstances, and for the side that makes the best tactical decisions to come out on top.
Exploiting mechanics like flight/charge and being able to completely ignore leadership auras destroys any semblance that Quick Battles could have to proper Total War battles.
The Causes of This Problem:
1) Leadership in Quick Battles does not work the way it works in campaign battles.
In campaign battles and all proper Total War battles, units outside of a leadership aura crumble and rout without accomplishing anything, and cavalry do this more readily than any other unit, making them glass cannons that lose to even Tier 1 infantry units if they happen to run into them while trying to destroy artillery and archers.
In Quick Battles, all units have self-sustaining leadership. This makes cavalry effective against all targets and means there's absolutely no reason to build a proper army consisting of infantry. Stock up on cavalry or flying monsters that never lose leadership despite running half the map away from any leadership aura, and you have an army that isn't at risk from anything on the field.
Furthermore, lords (whether on a dragon or on foot) should absolutely never be able to simply fly directly into the enemy army alone while their entire army is half the map away and succeed at anything. Yet they can. All because Leadership in multiplayer battles doesn't work as it's supposed to.
How is it supposed to work? Well, it's fairly straightforward.
Leadership is a stat that represents unit morale. Leadership auras are thus meant to represent the relationship between an army and its leader(s).
This is why in campaign battles and for as long as I can remember in Total War, units that went too far away from a lord or hero would fail miserably at anything and rout or outright break. By the same token, a lord or hero that dives into the center of an enemy army should also rout or break, or alternatively, the lord's entire army should rout/break if the lord performs a suicidal charge into the enemy army while his army is still far away.
These are the mechanisms by which Leadership and Leadership auras are meant to work. And it's how they work in campaign battles. But it isn't how they work in multiplayer battles. This breaks the fundamental dynamics of Total War battles, allowing for the exploitation of mechanics instead of proper tactical gameplay.
2) Lords on flying mounts are indestructible and are able to defeat an entire army on their own.
Anti-large melee units deal no damage to them. Armor-piercing ranged units deal no damage to them. Anti-large artillery deals no damage to them. Anti-large melee lords on foot deal no damage to them. Anti-large archer lords deal no damage to them.
Flying lords (and to a lesser extent flying heroes) simply don't take damage from any sources, allowing them to operate without any risk whatsoever and completely breaking the dynamic of any battle (as opposed to cavalry/flying monster squads that actually do take damage from all the aforementioned sources).
3) Cavalry/flying units don't get entangled, are able to disengage at will, and deal damage too quickly upon engaging.
The mechanics of unit entanglement are supposed to be fairly simple: if so much as a single model of your squad ends up engaged in combat with an enemy unit as you try to move it past, it's supposed to become entangled, losing its Charge bonus and automatically attacking the unit it ran into, thus forcing the player to give an order in the opposite direction and move away a considerable distance if they want to disengage.
This happens with infantry. This happens with monster infantry. This happens with lords and heroes. But it doesn't happen with cavalry and flying units of any kind.
Worse still is that once a cavalry or flying unit is engaged in combat with some infantry squad, it's able to disengage at will, preserving its health and leadership, thus removing any and all risk that's supposed to be involved in using cavalry and flying units to try and pick off vulnerable targets.
And for some reason, instead of the 10-15 seconds that the Charge Bonus lasts, cavalry and flying monsters are able to deal heavy damage within literally one or two seconds, leaving no room for reaction -- something that's not supposed to ever happen in a Total War battle.
The End Result:
Cavalry/flying units engage, delete a unit instantly, disengage, and repeat without losing any health and any leadership, all while outside of any leadership auras.
In other words, cavalry/flying units in multiplayer battles blatantly do not follow established rules and intended mechanics that are there specifically to prevent the exploitation of mechanics like this.
As a result, it's no surprise at all that every single player in Quick Battles uses armies that make no sense and break all immersion (75% cavalry/flying units/monsters).
How It Should Work:
1) Cavalry that makes contact with melee infantry instead of artillery/archers is supposed to lose leadership horribly and rout, because such a scenario is supposed to represent cavalry losing morale after a failed flanking maneuver while being far away from allies and the inspiring words of a leader.
2) A lord engaging an entire enemy army alone (regardless whether the lord is on a giant dragon or on foot) is supposed to either rout himself instantly or have the entire rest of his army rout, because such a scenario is supposed to represent an army seeing their leader perform a suicidal charge into the enemy force alone.
As in, the stats on the units in question shouldn't matter. Leadership as a mechanism exists specifically to prevent such abuses of game mechanics and stats. Yet it doesn't work the way it's supposed to in multiplayer battles.
The Suggested Fix:
I don't know why fundamental battle mechanics were made to work differently in multiplayer battles compared to campaign battles, but I do know one thing: the mechanics need to be made to work as they do in campaign battles and as any experienced Total War campaign player expects them to work.
I won't make the argument that it's unfair/unbalanced. I don't care about balance. I care about immersion. The simple fact is that battles against armies that consist 75% of cavalry or flying units, or worse yet, two dragons, a dragon-mounted lord, and three infantry units shouldn't be possible.
Clearly, budget constraints are not enough to dissuade players from using such absurd armies and destroying all immersion and quality tactical gameplay. But if CA fixes the aforementioned mechanics to work as intended, players will have no choice but to build proper armies, as attempting to use an army with 75% cavalry or flying monsters will result in instant routing, as will sending a flying lord directly into an enemy army without any support from any other units.