Thinking of Alchemy, Smithing and Enchanting, which one gives the smallest advantage to the player, e.g. doesn′t semi-automatically turning him into a god when combined with Archery or Melee on Expert/Master?

Any, as long as they aren't combined.

best-to-worst:
1. enchanting
2. smithing
3. alchemy

Also, you could focus on all 3 and give your equipment to companions. They do the fighting mostly.

Alchemy, really? Seems to be particular powerfull especially on an archer. Poisons not that strong? Invisibility-Potions are a nice advantage, too, for a pure archer.

However, I assume (correctly?) that Enchantment is the worst in terms of money-making of the Crafts, right?