I am under the assumption that Star quality % increase and Epic Levels (for those that have Defense % increases) are naturally being factored into Agnon's own attack damage increase against "high defense". Frankly, I think this is a bit over the top and suggest that these two percentage increases be removed from Agnon's damage multiplier calculations.
Inherent class increase to defense, e.g. Tank, is certainly in line with other inherent "extra-damage-to-X" passives, and rune defense increases does (I suppose) bring Damage Reduction back into potential consideration, so I can appreciate the conceptual balancing... of sorts. However, including the two percentages from Star/Epic quality in what consitutes Agnon's damage multiplier threshhold seems one step too far.