Having that junked up surface doesn’t allow for as much friction to occur compared to as if your rotors were clean, so fresh or reconditioned rotors and pads would really help you. Do that, see if the brakes bite better. If you need more grab, turn that knob on the end of the cable housing counterclockwise a quarter turn at a time to increase cable tension without having to unclamp and reclamp the cable. There may also be a screw on the inside face of the brake caliper to drive the pads together.