The problem is what if the arms tech doesn't want to do their best, but still wants a job. Say an immie wants their butterfly knives sharpened, a grandmaster arms tech may not want to just add 70 pts of damage of damage to something wielded by an immie. I know very little about relative damage, but an extra 7 pts of damage coming from a butterfly knife would be very significant, so an arms tech would be stuck using @holdback and knowing what number to dial in to what bonus is desired. A bit of a headache to keep a list of how much to holdback to what level. Especially if I'm doing this in a cube with a questionably violent person staring at you while doing this.
Perhaps a further system to be able to say how much extra damage you want to put in over how long of a time period would be something to look into? Maybe select how far you wanna try and then roll those cyber dice?