CAV dominates the battlefield for at least 100 years into the game. Once Landsknecht INF comes available (around LT 12), pure CAV won't be as useful but still stay strong.
It is a common mistake for beginners (no offense, well all started playing this game some day) to overestimate unit models. The few points from a unit model are mostly equal to a minor modifier for your dice roll. What really counts is the damage modifier. CAV has a 2-4 times higher shock modifier than INF. Due to the higher damage modifier, CAV benefits a lot more from good (shock) generals than INF.
What does this mean?
Well, in short 1 CAV deals roughly as much losses as 2 INF. Now the problem is: You can only fight with [smallest number of regiments on any side +4] regiments at the same time.
So imagine a combat with 10 CAV vs 20 INF.
12 INF will be placed on the frontline, 8 INF will stay in reserve and - do nothing until the frontline INF is mobbed up. So even IF you win a battle (you would need dice luck for that in 1450) by using pure INF, you will still suffer higher losses than the enemy CAV. The result of such a battle will usually be ~4000 dead CAV and ~10 dead INF.
CAV gives you more combat power during the early game per manpower. It gives you more combat power per frontage during combat. Until LT 13, there are three reasons to choose INF over CAV:
1) You want to storm forts.
2) You are so poor that you cannot afford CAV.
3) You fight offensively in difficult terrain (hills & mountains).
) - and since I didn't play vanilla anymore, I got used to the lower value...