I'm not a crafting tycoon like you guys, but i think we should point out the issues and let the developers find a way to fix them, instead of proposing systems.

It's obvious that going by gut feelings you can get to criticize something as fundamental in this game's design as crafting classes being as central as battle classes: you don't have the whole system perfectly laid out on paper like SE does.
So let's just say we want challenging battles like CoP and let SE decide how to make it viable in this system. If enough of us point a problem, it will be addressed eventually.

About CoP, i loved it, but the reason we won't ever get something as good as that was is because lots of people hated to be unable to defeat a capped instanced fight at the very first try like every other quest in the game and preferred to camp a NM that had impossibly long respawns precisely to avoid people camping it, or to farm gobbues all day long.
Difficult fights? Party strategy? Beautiful scenario? One of the best stories ever seen in a Final Fantasy game? Too much of a hassle.