Here's how Jasper works:
This is still true to this day and it's set into stone. I kinda understand why you want to freely change weapons without restriction but the balance in this game is because of the Jasper constraints. The legends are also designed in mind for Jasper constraints to make it fun and interesting but not too easy.
As for that visual DMG, that's not true DMG. It's just visual estimating the DMG. One thing that is true:
Chakram has highest BWD rogue. Gauntlet is highest BWD wizard. Hammer is highest BWD of warrior. That's for Mainhand.
The worst BWD for each class naturally: Warrior Sword, Wizard Wand (though barrage is very good with enough APS , Multi Attack, extra Attack , etc) and rogue flintlock (though flintlock is powerful with enough gear affixes like barrage is). That's for MH.
2nd highest BWD per class for MH: Warrior Lance , Wizard Staff and Rogue Bow.
The BWD that is 2nd worst but not the absolute worst of the weapons aka the 3rd highest BWD weapons: Wizard Sword , Warrior Axe and Rogue Dagger .
The offhand BWD remains the same for virtually all weapons but the shield has higher BWD than other warrior offhands but it also has 400% OH bash skill. Although hatchet also has bigger BWD by shield has highest.
Chakram appears to have higher DMG because you can cast 2 of them so that's why the visual damage is bigger but also the visual damage accounts for 25% item quality and APS. for any weapon.
Smoke bomb visual DMG shows 0 DMG but that's because Vault primary skill doesn't deal damage. Same with the Vial showing 0 DMG since Vial doesn't deal any damage either. However the special skills still deal damage of those offhand weapons such as smoke bomb. Stealth doesn't deal DMG but that can be changed using Amber crystal to any offhand such as Skulldraga , Torrents, Scalp, etc.
That's because the BWD isn't 0 for bomb weapon and vial weapon , otherwise all offhand DMG would be 0. Not just the primarys. The BWD of all offhand weapons virtually the same or quite similar except shield and hatchet. Warrior very good for offhand DMG for things like CV , scalp , skulldraga in arena .