If you want to play, and be aware of cav the entire round not putting you in any risk of dying to cav you can never enter a fight bigger than a 1v1.
You can argue that its all about the players awareness being poor that makes cav strong, but to me thats like saying a weapon isnt op because you only got hit because of poor blocking skills. There is no way anyone can be aware 100% of the time, and dropping that guard should not result in one shot death. Cav also decides where to fight, and if they are heavy cav they can make mistakes and often get away, while if the infantry messes up vs cav he pretty much dies or loses 90% health.
I think changing back the difficulty requirements on horses, giving them slightly better mobility stats but reducing health or reworking speed bonus for cav somehow would be fair, more risk for cav but let them have the high reward of oneshots etc.
Cav as is, seems to be the biggest deciding factor of battle. A group of 5 or so heavy cav can mess up an entire team so hard, its kinda silly.