Yep losing stats might be not that good, but considering the spirit power is more easier to get and more smoothly to upgrade, comparing to weapon power (Boundless Spirit vs Glass Cannon), it would be not balance at a 100% convertion.
It's good to mention that only in deep late situation this...
A T3 or T4 active spirit item. Active to switch between two status: 1. Convert 60% percent of your spirit power to 30% of your weapon power. 2. Convert 50% of your weapon to 25% of your spirit power.
Cooldown: 10s
If you got 100 spirit power and 100 weapon power, it will seems like this: In...