Did you check if your Warrior job soul is equipped?
Gunbreaker and Dancer are jobs only, so their job soul will be equipped when you equip their weapons, but warrior has a class (marauder) you switch to by just equipping the weapon and only equipping the job soul will grant you access to the warrior skills.
Try using equipment set to switch between you jobs, so you narrow the possibility to accidently unequip your job soul.