How the hell i use cavalry?

They are extremely weak!? I know i shouldn't charge infantry lines from front or squares but even when charging from flanks or rear, my cavalry lose heavy casualities. Stay in melee or cycle charge doesn't matter, enemy line infantry just slaughters my cav.

And line infantry seems to fire 360 with no problem. Even from the rear, first can fire backwards. Is cavalry only useful for running down fleeing units or am i doing something wrong?