I agree with basically everything here, especially point #5. Once I unlocked a few high tier sword pieces I am able to craft incredibly expensive and powerful two handed swords with only a tiny performance penalty. I don't think a hard skill limit is the best option, but there's need to be a much bigger penalty to the performance and price of the weapon that is made.
For example, I have a smithing skill of 50, but I can make a 2h sword with a difficulty rating of 130+, using raw materials that are extremely abundant (from smelting low-mid tier weapons), and I can sell if for 4000+ denars. The penalty I get from having a low smithing skill is negiligible and only results in about a 2% penalty to my weapons stats.
This alone breaks the game economy because no other source of income matters anymore. My tax revenue, my trade income, the money I get from selling plunder of war are all pocket change compared to the amount of money I can get from selling 4 or 5 custom made 2h swords made by my novice smiths.