In the save editor, when you highlight the Enchant Weapon skill, can you click on the up/down arrows beside the box where it shows the current skill level?
The stats on the dragon and Larian breastplates are random (as with all other equipment), so in any given game one may be better than the other, or better suited to a particular character class or playing style.
You only need to wear the complete dragon armour set once to complete that quest and get the reward. After that there is no additional bonus for keeping it together, so feel free to mix and match depending on what other armour you can find or buy.
