No the real problem is that sorcs don't get ANY benefit to their melee attacks or stats from willpower. Sorcs do however get bonuses from strength. This relic would work fine as is if sorc's actually got the melee stat bonus from willpower like they should
Then how do you explain the sentinel's result? They got both force and melee affected by their strenght.
That means the relic does an attack that is considered damage on its own, and not an extension of the attack that made it happen.
From the info, its something gunslinger has, and neither sent or sorc got, and all "unrelated moves" in the game (valor-unlockable melee "attacks" have been put down as tech. Makes sense that they might have coded the damage as "tech" coming from an item.
I bet it procs yellow numbers, right?