I was referring to the X2 leveling. You'd still level both up at the same rate.
Overall leveling.
Say one of your major skills is nlade, and you use a sword.
Level that skill up once, 1/10 of your level done.
Use a blade AND an axe while two of your major skills are blade and blunt.
Level both skills up at the same time, 2/10 of your level done.
Progress faster, also kill moves look lovey.
Though the most we've seen is kicking a doge and stabbing a person in the chest.