Amon, are you sure on that part?
If I got lets say, L 100 tinkerer. And start a with lets say L 1 Blacksmith I do not get XP for making lets say, Bronze Bars. I maybe can make Mithril or Cobalt Bars but it surely does affect my character and my other Craft schools - from that point of view its nice to have an option to drop a Craft school like we can drop Adventure schools