A melee warrior would invest himself in his armor/weapons and the only crafting profession that would make sense is Blacksmithing. Think like a warrior, live like a warrior and you won't be using things like enchanting and alchemy to furthor augment your gear to ridiculous levels.
If you're a mage you focus on your spell schools and enchanting. Your spell damage doesn't scale as well as a melee weapon but your stun-lock perks, summons and severe magicka cost reduction make up for it.
Finally we have the stealthy theif who can front-load the most damage of anyone but doesn't have the defensive and restorative capabilities of a warrior or mage. You create poisons and sneak around, but you don't make sense as a smith or enchanter.
Now this is a completely open game where you can mix and match whatever you want to varying degrees of overpowered or unviable, but what I just described is where the balance is. Break that balance at your own peril.