Engraved gothic plate was decorative. Most of the armor we still have from the middle ages is decorative in nature: If it wasnt pretty, it got melted down and reused. No one entered battle (except stupid nobility) wearing such armor.
If ya dont think armor that remains is not decroative, check out King Henry the VII's cod peice at
http://www.hrp.org.uk/Assets/Cod-piece%20(mp%20asset).jpg. FYI, the cod piece covers the groin and is designed to be removed so one can relieve themselves without removing all the armor.
I too have done SCA combat. Everything is effectively a club. Being hit hard in the head, many times (the head is the open spot for new fighters, it takes abit for that to get trained out), I can tell you having a big solid metal thing over my head allows me to type this message today. In the order of how I would precieve each blow:
No helm: Unconsious.
Helm with no padding: It would really hurt, be loud, but would not disable.
Helm with inadequate padding (my helm for a while): As with normal padding, but the occasional blow would cause an edge to dig in and I would bleed.
Helm with adequate padding(1/2" closed cell foam, usually made from cheep blue camping pads): Annoying to get hit in the head.
The worst hit I took with a club to the head was full speed from a guy who was known to hit hard. The shot almost knocked me over (I am 6ft, he was 5'6") and my face just stung.
A big factor in how effective the helm perfromed, in respects to a club, is the weight of the armor. DF has this wrong if the lightest stiffest armor is considered the best. SCA combat helms min weight requirement is 12lbs. Someone made an experimental aluminum helm that weighed 4lbs, he used it long enough to take 1 hit, and never used it again. Almost broke his neck.
Understanding that playing with fantastical platinum hammers is a nice fantasy, but DF does not take into account the energy it takes to swing a weapon of that mass. An effective combat weapon for me weights all of 4 lbs. I do not have the muscle mass to do much more. The effective combat weapon for.. lets say the Rock... might be 15lbs. Yes, I could swing the Rocks hammer a couple of times, but combat is more than just swinging the weapon. All things being equal, If I were using a 4lb weapon and my opponent is using a 15lbs weapon, his swing frequency will be so slow I can ignore the weapon and just attack him.
Materials do not dictate outcomes either. I retired my first helm after getting crease from an overhead wrap and the crease popping a weld seam. The club was made of rattan (a wood) and the crease (you could place the club in the spot and it fit) was in the 12gague steel crown. So, a piece of wood properly used, can break steel.
The true defeat to plate armor are piercing weapons. The piercing weapon focuses all its energy into a small area to do the damage. This is true weather the source is a bullet, a sword thrust (a trained fencer can put the tip of his 4' long rapier in a 2" hole 6ft infront of him, an eye hole is a common target) or some spike attached to a pole (a war hammer).