I think the important thing to consider here that each value for a weapon has to lead to interesting trade-offs. Each value should be particularly useful for some reason, and should carry accompanying limitations.
Your club/iron helm combo there is an interesting example. By those rights, I would be better off using the dagger against that helm, but a mace is actually a much better weapon against most types of armor than a blade - softer armors moreso than rigid ones, but still.
In order to get the right mix of "Easy to use, difficult to master", you also have to ensure that there are tactical combat situations where a high rating in any of the values is particularly useful.
So, assuming weapons have those 4 values:
1. Attack Rating - universally good, but adds to overall cost of weapon, and requires higher technology level to create. So low attack rating items are more common at lower levels and cheaper, allowing for more people to be equipped with them.
2. Damage Type - most basic ones should be available from the get-go - piercing, slashing, blunt. Do damage types stack, or does only the highest apply? Could I do a "Club w/spiky bitz on" (3 attack, blunt damage, melee) (1 attack, piercing damage, melee). If you can do stacking damage types, how many can you add?
Again here, we're looking at a cost and possibly a resource requirement - blunt stuff is pretty easy, but a good slashing weapon takes some metal, unless you want to be replacing your obsidian a LOT - yeah, I'm looking at you, macuahuitl.
3. Range Value - would this be a value of tactical map squares? Would it be possible to assign a range (2-10 for javelin) and have penalties for being under it? I'd like to see some sort of system here that rewards short swords in tight melee combat rather than just "bigger is better". I know in tight formation the gladius kicked the crap out of the gallic longsword or a spear. Or will this be where combat speed modifier comes in?
I'd love to see the range value also have some effect when units close on each other, and a starting 0 number, which indicates shield-to-shield. That way, you could have a pike unit being attacked by a shortsword unit. Pikes have combat range of 1-3. So they attack the shortsword unit at 3,2,1, the shortswords have range 0 - all of a sudden the pikes have a -3 (or whatever) penalty and the shortswords are cutting them up.
4. Combat Speed modifier - ascending or descending scale (is 1 good or bad?). Combined with Range value, this could be really interesting. A speed 5 range 0 weapon like a shortsword vs a Speed 3 range 0-1 weapon like a longsword would be interesting.
That's my thoughts, just as a start.