Wait........legendary skills is really just about perk points? it doesn't actually make your skills more.....powerful?
This is true, resetting a Main Skill will cause a character to become a Novice again, and the character will have to relearn the Skill from usage, or Skill Trainers.
SquattingTurtle, resetting a Skill resets Perks, a Skill needs to be relevelled and reperked to be as effective as it was before it became a Legendary Skill. An enchantment can increase the amount of inprovement on a Crafting Skill, but without the relevant Perks an item will not be as affected by Smithing/Alchemy/Enchanting.