Basic materials such as Iron have too much weight in the crafting system and tier 2 or higher crafts actually end up taking more money and more materials for less mathematical xp. it makes more sense efficiency wise to small low level crafts to level up crafting skills.
Tier 2 and higher crafts should give a lot more xp per craft than they do probably by 50% to make the case to craft them over tier 1 Iron crafts. Another solution is to require tier 2 materials such as Steel to use 2 Iron Ingots in their synthesis instead of 3. This would move the efficiency to Steel weapon/armor crafting over Iron as well.
Example if an Iron Rapier costs 8 Steel ingots to make and gives 520xp (estimated because its maintenance) thats 24 Iron Iron Ingots AND 8 Sand Flux. With 24 Iron Ingots you could craft 3 Iron Rapiers for 200+xp (estimated due to maintenance). Thats still a 80xp+ gain by just doing old recipes.