Being fairly experienced as cav (been playing it for over a year), I'd say that the standard anti-cav tactic of a square/blob/circle is pretty effective... if executed correctly. When fighting infantry as cav, a head-on charge means you die 9/10 times. Going for infantry not aware of you, means he'll die 9/10 times.
So as long as the infantry regiment stays together, facing outwards, counting on their regiment member to do the same, it's fairly easy to keep cavalry at bay, as long as you stay focused.
The main reason infantry regiments in this formation are easily killed, however, is that certain members of the inf regiment grow impatient, move out to kill a cavalryman, and get slashed from behind, leaving a hole in the formation, through which the cavalry can charge, decimating the regiment.
So as long as the inf regiment sticks to his formation, and stays focused, the cav will be held at bay, and when some men are inside the formation shooting, the cav can be dealt with effectively from range (even when just shooting their horses).
So is cav OP? No. But they do have the easier job, as they don't need the constant vigilance the infantry needs.