That way you create a sink for stamina
And you give a perk for having stamina
Also when you have no more stamina it cost twice as much mana
And when you don’t have mana it cost twice as much stamina
Melee and bow is now way better by having a damage boost and a mana burn/mana deficiency mitigation, he sacrifices power to compensate
Example values: you have 1200/2000 stamina left, if the ratio is 1:10, you get 120% increased physical damage with attack
Vigor now becomes a nice aura, Harmony because interesting
Increased stamina skill on barb now also becomes a source of dmg and ressource
Now sources of stamina and slower stamina drain become interesting attacker choices like Eld rune, Vidala boots, charms
To be clear, the stamina cost isn’t an extra cost for attack, it’s just a payment to access the Damage bonus