Well, any nerf is welcome. The current implementation brings too many advantages if distributing Diamond Dragons to different heroes.

Another thought about the balance of Diamond Dragons is its stack exp ability.
It has a never-working SE ability from WoG: 100% to Deflect 0-50% physical damage until igrik/daemon_n fixed and let it work again in game bug fixes extended.dll last month.
The fix brings a problem. From what I can see, the stats of Diamond Dragons are balanced considering this Deflect ability not working. Now since the Deflect ability works again, Diamond Dragon in full stack exp has become way too stronger than the other level 8s. I have done some tests in battle and with no doubt Diamond Dragons is the strongest. This is not good because they are much worse in 0 stack exp competition. The growth of strength is a bit inconsistent. It doesn't make sense that stack exp changes everything of this creature.

My suggestion: Reduce the chance of Deflect from 100% to 30% or so (Reference: Hell Hydras have 50% chance to block 50% damage on Rank 10). Having to watch the animation of Deflect each time Diamond Dragons gets hit is torture. A lower chance to trigger the ability would just fit.