agree - the Promax mech discs are bad - one of the worst performing brakes I’ve ridden in recent years ... that includes low end cantilever brakes
I would consider switch to Spyres (or Avid BB whatever .. BB7 ?) ... with a decent pad (Swiss Stop ?) maybe they will provide better braking but would not go too far - a standard / straight gauge steel frame is not worth sinking much more $$$
Yup. The Promaxes are essentially BB5s -- they share the same pads and horrible modulation. But IMO, BB7s are at best a "lateral" upgrade; single-piston brakes just require a lot of caliper-fiddling and/or rotor-truing; especially with QR wheels. A set of Juin Tech hybrid brakes might be a good alternative. I agree on not sinking too much into the bike, but mech or hybrid brakes can be moved to a new frame.