You two are talking about the same thing, except that ThornKiller is subtracting defense from accuracy and Confidence is subtracting accuracy from defense. The final numbers are the same.. the only major point that ThornKiller is trying to emphasize is that your hero can actually have a combined defense above 95%.
On a side note, I thought I read recently in the updates that they did add a cap of 90% defense to heroes.. but I just looked through the updates again and didn't see it.