The Defense softcap for Incarnate content is 58.75%.
So long as you're fighting enemies within 5 levels of yourself, the softcap remains the same. Critters between 0 and 5 levels above you gain accuracy bonuses from the purple patch, so although they do have a better chance of hitting you, it's not something that more Defense will help with.
Of course against enemies with to-hit buffs like Tactics, the more def you have, the better.