Mirrorrorrim
Hero
Currently, the designers think the "at-will" level of power are already represented by the current Weapon Mastery system being playtested. Are you suggesting that those are insufficient and deserve to be more powerful?I mean why even limit it? If Casters get to cantrip forever, so what if a Fighter is proficient with x weapon, it gains a bonus effect.
If its OP (and I doubt it highly) then just say you reduce the damage, or you get a bonus to hit for 'just a normal swing'. Simple stuff.