That Metamorphosis issue is a big one for example.
It WAS a key, signature DH ability.
It IS a key, signature Warlock ability.
The armor issue? Deconstruct is a good idea. But it still leaves the class sharing one of the druids flaws. That they don't change their visual appearance, they don't get to change their look or show off their gear. Nor does it readily hook into Gems or Enchants or transmog.
Resource and combat mechanics can be developed from scratch so that it can end up very different in feel. But the problem is you still end up with class that either fills a niche already filled (the issue GC brought up) or isn't a WC3 Demon Hunter.
And you said it yourself:
Well I structured my DH class as more of a battle-mage type of class.
Why not simply call it a BattleMage?