You can have as stiff a spring as you want, provided that the contact surface of the working spring arm is polished, to reduce FRICTION. And, then the cam on the bottom of the frizzen has to be polished to reduce friction when it rubs against the spring. Finally, you have to control the amount of movement of that spring arm on the frizzen spring, to reduce the amount of force needed to open the frizzen Quickly, so that sparks are Thrown down into the flash pan, NOT DRIBBLED down the face of the slowly opening frizzen.
It helps of course, that the pivot pin/screw on the frizzen be oiled, and working smoothly. Without that pivot being attended to, all the other work is not very effective.
The ONLY 2 reasons to reduce spring tension are: 1. to stop the severe rattling of the gun barrel and sights when the lock is fired, as all that energy IS transferred to the gun barrel; and 2. to reduce the amount of damage done to the edge of the flints( "eating flints").
That latter point doesn't seem to matter to all flintlock shooters. But, in today's economy, with the cost of flints running a dollar apiece, it does matter to many flintlock shooters. I only include information on the subject to help them achieve their goal of having the least expensive, Large bore caliber rifle they can own and reliably shoot to take big game. If you like replacing flints after every 10-20 shots, knock yourself OUT!
You are correct about the angle of the frizzen face being adjusted to a correct arc. It is important( and lacking on so many locks). For most flintlock shooters, they can't afford to replace an existing lock with a custom designed and made lock, so they are left with making adjustments with the existing frizzen arc, and with the height of the existing Hammer( cock). :hmm: