Sub weapon mastery growth

[Ragnaman]

If I equip gloves as main and sword as sub weapon, will i raise mastery with both weapons ? Or it depends which weapon i am using ?

I read that having 2 weapons is beneficial because you can have more tactical options when both are trained (gloves having specific aoe and swords having specific aoe, etc.).

[Pickleton]

It will only raise the one you're using.
Honestly, I never really bother with subweapons outside of unique innocents.
In general I want 1 person to have my best fist weapon, so having a character with both swords and fists would cut into that. It would also mean that you're leveling your weapon skills slower, because they're split between the two.
The only exception I make outside of late post game would be giving a cleric a bow with a staff as an off-weapon in case I need just a slight bit more oomph (or range) on a spell.