If the counter weight was locked not to rotate, the pin on the weight that sits in the slot rotates in a small circular motion if viewed from above. As the weight moves outward that pin moves in a curved motion to the new position (not linearly) and makes a larger dia circle in motion. At full advance it is tracing the largest circle. The force that pin puts on the cam to make it rotate is not perpendicular to the slot, rather angular as it curves outward. Lower force applied in the direction of rotation. A cam with an angular slot actually changes that force to perpendicular against the cam slot. Which means it takes less force to move the cam, which means the springs can be heavier and still get the same angular rotation at the same RPM as straight slot which has a lighter spring. If the spring is the same on both, the angular cam will rotate more at the same RPM and get advance in faster.

So besides effecting how much rotation is allowed because of the angular slot, it also effects the force on the cam.

I was confused on your slew rate comment.

We are making this more complicated then needed, and clearly folks think one is better then the other.

I never thought some one was doing this welding up to tune all aspects in one shot. Set initial timing, effect spring rate, limit mechanical. But I get it.