I feel like the cavalry (knight, horseman,etc) are a bit too many in my opinion, for example , the first crusade got around 35,000 soldiers (30,000 foot soldiers and around 4,000-5,000 cavalry) which means the amount of infantry is far outnumbering the cavalry one. But, I found that the amount of infantry and cavalry of both my allies and enemies forces in any battle are almost even (1:2 ratio for example).
Maybe if the cost and wage of cavalry (mercenary horseman also and especially knight) being raisen up, the amount of cavalry we have and AI will be proportionate similar to the real life one , but this is only my opinion and suggestion although I myself are cavalry loving one.