as picture above i test its with my cannoneer
test with skill cannon shot lv1
the damage when equip with Xbow+arde dagger is around 6.5-6.9k while
the damage when equip with Xbow+Cannon is around 7.4-7.8k
from what i found the damage skill of cannonneer only improve when you equip the cannon in sub
if you not swap weapon to cannon before using skill its will use your base damage + current sub weapon (in this case its arde)
yes you can using its with other sub and the animation looks like its auto swap for you but damage is not include in its
thats why some say thats even you use Agvara Cannon the damage will not improve
I dont know if musketeer be the same or not (dont have musk for test)
but this is intent or not?