IGD lead versus JKA lead P1 Retribution team

TMK

Living in an uncertainty, I decided to clarify what works better here.

The setup I am running is either JKA (L) with JS, Maul, GK and FOTP or IGD (L) with rest of the team the same.

Here is my concern;

IGD inflicts Defense Down and makes 100% more damage to the Droids, thus he inevitably does more damage than JKA.

BUT

JKA leader gives whole team 15% Offense, 10% Critical Damage (30 and 20, respectively to the Jedis) and Offense Up (50% Offense) by using his Special AoE. This would mean the rest, excluding JKA, do more damage than they would under IGD lead.

Therefore; why is IGD still preferred leader for such team composition? How does debuff Defense Down actually work? What are its mechanics? Is 60 or whatever defense IGD leader gives a game-changer in particular case?

Has anyone tried, experienced, worked on this?