I would also like the possibility of "on hit" properties like Armor of Agathys to trigger on a "miss" that was an AC deflection. It's a bit counter-intuitive for such a protection to only work when you take damage, which you're trying to avoid anyway. You try to pump your AC as high as you can, which actually makes those protections not trigger.
Armor of Agathys doesn't increase AC, it gives temp HP. That's why it makes sense for a protective spell to have a damage trigger when being hit. I still agree with your larger point (or mrfuji's, I guess) that everything missing the same way should be adressed.
