Yeah I forgot that horses can trample people while jumping over obstacles and can charge in very tight locations like inside buildings or trenches, silly me. Seriously, whats your problem?
Horses are animals, not trucks -- they can go wherever they can fit. Been to Napoleonic-era forts that were built to incorporate cavalry.
As a casual cavalry player and a part of 99% of the community I usually get a KD of about 4-20. Cavalry is certainly not 'balanced', my dear friend.
I usually get very good KDR as cav (only slightly less than charging around aimlessly with a bayonet).
I fully agree with those who are mentioning the psychological effects of cavalry; IRL, cavalry are OP. They are also, however, very expensive to maintain, require lots of training for the horse and rider, and are controlled by the horse's brain instead of WASD. In NW, people and horses are fearless and have unlimited stores of energy, in addition to being able to perform at full capacity while severely wounded. No one is going to win a realism argument here. The balance between horse and inf in WB and NW does not reflect reality, but it IS a balance. A very skilled cav has never been able to take down an equally skilled infantry 1v1 in this game -- if both of them know what to do it will be a stalemate forever. Cavalry perform very well (in this game) when they avoid direct 1v1 combat, and unless they make the cav system much
more sophisticated, its going to stay that way. That doesn't mean they're "rubbish", though. As FloorBelow confirmed, its easy to get very good K/Ds as cav if you know what to do.