I read quite a bit on army composition, and the general opinion seems to be that cavalry are utterly amazing for the first 150 years. However, 100 years into the game (land tech 13 if memory serves), just looking at the stats, my infantry is much greater at shock, fire, and morale in all aspects. Latin Knights just seem useless looking at the stats, yet they cost twice as much to recruit and maintain. Am I missing something that makes cavalry much better?
There are modifiers much more important than the unit stats shown in the military screen. These are the fire and shock modifiers from your land tech level, shown next to your current unit model. In general, CAV has twice the shock modifier of INF during the early game, so it deals (roughly) twice the normal damage in combat. This means CAV will give you more combat power per manpower (which can be important for many small and medium sized nations).
Another advantage is that it provides more combat power per frontage: During combat, units are placed in a line facing each other. INF is only allowed to attack a unit in front or one square next to it, CAV may attack 2 squares away, ART is allowed to fire from the 2nd row (with 50% of it's regular firepower). All units that cannot be setup in range during combat will be placed in the second line (reserve) and do nothing until a slot in the frontline opens. This makes CAV even more powerful, let me give an example:
You have 10k CAV, your enemy has 20k INF. Both armies cost roughly the same amount of gold to build and maintain (but keep in mind most natios start with high aristocracy, which makes CAV a bit cheaper than INF in regards to firepower per ducate). But while you can place all 10 units at the frontline, your enemy can only setup 12 INF - the remaining 8 regiments wait in the reserve, doing nothing. So the frontline combat power is 20 (10 CAV * shock modifier 2) vs. 12 (12 INF * shock modifier 1) - despite being outnumbered, you will inflict more casualties to your enemy (assuming both have the same dierolls). In addition, if you have a good general, you will deal even more damage with a good die roll.
Another thing to keep in mind is that there are two ways to win a battle: First via morale and second via casualties. INF armies will usually win against pure CAV via morale (esp. once landsknechts are available), but pure CAV will almost always deal more damage until the tacticas modifier is increased for the 2nd time.
This was how it worked most of the time, but this made CAV quite overpowered, so paradox has build in some measures to reduce CAV effectiveness:
(1) There is a modifier called "tactics" that reduces damage taken if you have no more than a certain amount of CAV (40% for latin nations iirc?) in your army. It gets larger as tech progresses and makes pure CAV armies much less effective.
(2) CAV receives doubled terrain (and river crossing / landing) penalties, making them much less effective on the offensive (!) in difficult terrain.
(3) Fire now comes (once again) before shock, so once INF and ART have decent fire modifiers, they will basicly have 5 rounds of ranged combat where they can maul CAV (since CAV has an abyssmal fire modifier and deals almost no fire damage).
you really only need 4 cavalry per army for flanking.
INF can flank since HTTT, so you only need 2 CAV per army.
