The mobility and speed of light cavalry? Check. Camel Gunners really are in a league of their own.The Moors also get Camel Gunners, which are essentially mounted musketeers, and start off close to Timbuktu, where a few merchants can make several thousand florins per turn. Sure, you don't get them until late in the game and all the other infantry the Moors can field are mediocre, but their baseline stats of 16 attack and 22 defense, low upkeep and good morale and stamina more than make up for it. Think Highland Nobles and Noble Swordsmen are bad? Try the Moors Dismounted Christian Guard unit.Pair Highland Nobles with some Noble Swordsman for shock attacks and a bunch of pikemen to ward off cavalry or accept counter-charges, and you'll destroy nearly everything. Scottish infantry are some of the best in the game, especially on a charge, and are pretty cheap compared with most other factions' infantry. Cavalry are squished outright by the range of pikemen that the Scots can field. The reason for this is because when you've got 1,200 screaming, painted, claymore-swinging Highland Nobles charging you, no amount of arrows or bullets are going to save your ass. The Scots don't get high-end gunpowder units and have relatively weak archer units.Also, the Scots have Highland Nobles which, when fully upgraded, cleave through most infantry and cavalry like a chainsaw through tapioca. The Scots have access to Noble Swordsmen, who are basically Dismounted Feudal Knights on steroids.It will almost guarantee winning against any other stack of army costing the same or even more, provided that general skills don't differ too much.
Also, Dismounted Feudal Knights are probably the most effective unit in auto-resolving battles, so if you feel not confident in controlling a huge army you can just spam dismounted feudal knights and auto resolve.They're also incredibly vulnerable to a direct cavalry charge. They're eventually countered by crossbows and gunpowder. These powerhouse infantry units have insane defensive bonuses and are very effective in close combat. Arguably, the Dismounted Feudal Knights are an early-game Game-Breaker.
The Russians may also qualify: while they start with the weakest roster of any faction (and territory that is difficult to both conquer and control), any city of theirs with the Huge Stone Walls upgrade can build Cossack Musketeers, a top-tier gunpowder unit, the instant blackpowder weapons become available.Firearms also pierce armour like tissue paper. If sheer number of men killed in a single go won't cause rout, then the debuff will. Musketeer ashigaru, when firing at troops right in front of them, will simply slaughter whatever is in front, while survivors will be under the debuff effect of firearms to morale.