The geometry of the calipers themselves look fine. (I love the old Mafac and near copy old Shimanos with their horizontal arms. You have nearly that.) But I would can that cable. Get a standard brake cable and a cantilever bridle that has a ball or puck on one end and just bare cable on the other plus the triangular straddle piece that clamps to the brake cable. Set it up leaving all cables long. Ride it. Play with the bridle cable length and the amount of post on the brake pad showing. You will find you can get quite different powers and feels. (I find I often like my bridles long. Not as crisp feeling but lots of power to dry wet rims. And in panic stops, I don't go over the handlebars; just stop really fast.)

And as other said, get KoolStop pads. Yes, there are other good pads. But with KoolsAtop you know you are getting good pads. Also that if you still cannot stop, the issue is elsewhere.

Ben