First, The Nightmare Dragon and King of Korne are contenders for two of the hardest enemies in the game. They will stress the combat abilities of any build. But let's check out a few things.
You have AGL 6 but DO NOT have the Advanced Skill Flurry. That seems odd. Typically the only reason to get a Warrior to have AGL 6 is to learn
Flurry.
Infantry Training only works with 1-Hand weapons. Not Light weapons. So a better skill point allotment would be something with STR at least 1 or 2 points higher than AGL. (Obviously more if using 2-H).
The Nightmare dragon hits with heavy death damage and the King of Korne hits with heavy fire damage. So making sure you have serious fire/death protection will help a lot. Use those elemental protection rings, items, potions, etc. You don't say what your equipment is so just tossing that out there as some players forget that crucial aspect.
You don't mention your Companion choice, but given your character build, Hirge with a healer build might help out a lot. You do the damage. She helps keep you alive.
In general, elemental resistance potions will make more of a difference in a fight than a shield potion but that is mostly due to resistance potions lasting for a full minute. Let's do some math. A Shielding Potion gives +10 armour for 12 seconds. Using a shield gives you 4-to-10 points of defense for an average of 7. So if you get hit once per second (attack speed 10), that means on average you could expect a Potion of Shielding to reduce your damage by 84 points (7 x 12) over those 12 seconds. Not exactly outstanding but notable. Toss in the fact you can use other potions on top of that (healing, damage, etc). It can tip the scales in your favor.