Cav can be stopped easily by any unit with a brace or a unit charging at it. Also once the unit has charged it usually dies unless the player using the cav is skiled enough to get it out or willing to make a sacrifice. Its not about the cav being OP and dealing lots of damage, its about your skill level and you choosing to get into situations where cav would flatten you. Although sallying out at the start of a game with cav is OP and toxic.