I just tried 1 AAA fight.
Iron Eddie ( guard immortality), Sekmeth(Thief, Strike), Icarus ( destiny shell), Assassin Hellriser(eternal)
I tried with 4 fully sharded and fully equipped characters including Ancient Mariner and Magus Lilith and lost. 2 Destiny sets didn't get a single Invincibilty for me and gave it to Icarus immediately. So it seems for computer it is not broken.