I'll directly answer your questions first, then provide tips.
- If I legendary the one-handed skill and it resets to 15, do I have to again get it to skill level 80 to get the double damage power level
Yes. All your perks related to the skill are refunded.
- Since my attack pattern is nearly exclusively one-handed, is it any use for me to reset the one-handed to 15 and get hit with a "nerf" in
one-handed damage? (i.e) Do my one-handed damage decrease on resetting
Your damage does decrease due to loss of perks and skill level.
It is not a good idea to reset any of the melee combat skills because they take a long time to level up.
I'll start with a trick that doesn't require Enchanting, then one that is the fastest way to get 100.
Prerequisites for fast leveling are:
- a bunch of gold
- expert trainer
- *optional* some pickpocket enchanted gear
- Use trainer
- Pickpocket gold back (save scum)
- Repeat 5 times
- Reverse pickpocket items/gold
- gain pickpocket skill until you level up
After hitting 90, reverse pickpocket some more and get 100.
Just got to watch out near the start that you don't give the trainer so much gold you can't pickpocket them back.
You can reverse pickpocket items and gold to repeatedly gain experience.
Note: If your game is unpatched, Fortify Pickpocket enchanted equipment can reduce your pickpocket chances.
The best method
- 90+ Illusion skill
- Complete Grandmaster quest and buy Harmony
- Enough Fortify Illusion gear so you can cast Harmony at 15 skill
Go to Whiterun, near the outdoor market outside the Alchemy shop. Cast Harmony. First cast gets you to 50+ skill. It takes you maybe 8 casts and you'll hit 100.
Getting to 90+ Illusion isn't that hard. Some Fortify Illusion gear helps. Cast Muffle (apprentice) everywhere will raise the skill pretty fast. You can equip it on both hands, but just make sure you release the spell not exactly the same time so you get the experience twice.