Zethnos
Explorer
The fact that other characters *can* get the same starting AC is irrelevant -- this is giving it to them without any investment (in class, or stats, or feats, or spells).
Your discussion begins to outline why the spell is so poorly worded; it is something that has been discussed on these boards previously, and that's part of why I don't like it here.
Even though you don't think it's powerful, it is still a concentration-free, no-duration-limit second level spell. AC12+dex (~leather, less than dragon hide) is what I would suggest instead.
So here's the thing... Dwarves exist... and also... This exists. http://engl393-dnd5th.wikia.com/wiki/Protection_from_Poison
Are Dwarves overpowered now?
Also I rewrote the description of the natural armor if you want to take a look.