Yeah, like @Slypenslyde said: something needs to be done, I’m just not 100% sure what that solution should be.
As I’ve said before an upgrade should feel like an UP-grade. Instead, I find myself going: “I can only upgrade to [insert relevant number here], otherwise I’ll ruin the weapon.”
I shouldn’t feel that way about a supposed “upgrade”. I should be excited that I can up my weapon, not afraid of accidentally upgrading it too far and making it worse. That’s just poor game design. As I said an UP-grade should feel like just that, an improvement.
Also, because weapons are tied to Kingdom Power, this presents another issue, currently. Eventually, you might find yourself “upgrading” weapons you don’t want to, just to get another Star for Kingdom Power. I mean, hooray, you got that extra star/reward, but it came at what cost?
In my opinion, it would take a HUGE reward, for me to, essentially, ruin weapons like my Dawnbringer and Divine Protector. And, even then, I would still be extremely hesitant to do so.
Also, on a related note, why are some of these weapon upgrades so stupidly attached to weapons that don’t benefit from them? For example, one of Mang’s “upgrades” is “Create a Red Gem”? Why on Earth would An Armor Destroying Weapon need to create a Red Gem? That would be way more useful on something like Divine Protector. At least, in theory.