Defense doesn't affect how easily a unit is hit, it subtracts from the damage taken. Dodge is reduced from accuracy.

Let's say the enemy has a group of archers with accuracy 80. If you are on horseback, they will each have an individual chance of 55% to hit. After that they get a  damage number based on a roll of their attack. Then you roll for defense and deduct that. If total damage done is zero, as is probable in your case, you should see a 'Clink' displayed.

I'm actually not 100% sure that to hit rolls are not group based. I see groups with 70% hit chances miss very often.

Accuracy of group units (multiple units in a stack) is calculated separately. So basically, if you get a group of 7 archers shooting at you, they get to roll hit 7 times, this means you won't see them "miss" very often. However, when those units roll a "miss", they don't contribute their share of the damage.

In example: A group of 7 archers, who would do 10 damage each (to make it simple), 5 of which "misses"... the game will still show a "hit" but they will only do 20 damage instead of 70.

Basically, you are getting the effect of the miss, but you're not "seeing" it. The only time that this is troublesome is with backswing units.

I also see ranged shots miss frequently. I have no idea if the the dodge mechanics are working correctly, but I do know that I see the shots miss frequently. Also, I notice that you said that this was a late-game scenario. This implies that the units should be relatively high level (which grants an accuracy bonus) or trained in a fortress with troop boosters (some of which grant fairly significant accuracy bonuses, others that boost initial troop level). As I understand it, the dodge mechanic is something along the lines of

          chance_to_hit = attacker_accuracy - defender_dodge

It isn't that hard to boost accuracy to the point where you'd be looking at 90% or better hit chances against most units. It would help a bit if you determined the accuracy rating of the units attacking you and compared it to the dodge rating of your units - if you've only got about 30 dodge (total) and the enemy had somehow achieved trained units with, say, 130 accuracy, a nearly 100% hit rate is entirely reasonable.

Also, champions are very bad things to use as a comparison for accuracy - they get levels much more quickly than anything else in the game, and they have the ability to gain significant boosts to accuracy and dodge. Beyond that, they have some traits that can increase the per-level bonuses to accuracy and dodge.