To some extent I've used double lines of infantry, so the first line gets hit and the second line attacks, but it's not an ideal solution at all as cavalry can pull back. I would agree that cavalry charge head on is far too strong in that there isn't really anything apart from pikes that can withstand it. I've seen too many games that involved wiping out an entire line of infantry with a cavalry charge from multiple units and then proceeding to fight the cavalry behind who get the morale penalty from routing units. Yes cavalry needs a clear line and needs to be facing, but it's not that hard to accomplish, even easy for frontal attacks.