Not yet mentioned is the actual situation at hand, blaming people doesn't change the situation.

The bike has many of the worst cases for effective brakes. Chrome steel rims which have less friction for the pads to work with. Long reach caliper arms reducing the leverage. Not known but a likely assumption is that the replaced calipers are also more flexible then the steel calipers that were original. Also that the pads are likely old and/or low grade. Then there's the cables. If the OE ones they have a fair amount of friction, not being of lined casings or redrawn inners. Last are the levers with limited travel.

Combine all these factors and it's no wonder to any one who works with bikes that the brake effectiveness sucks. Any mere mechanical adjustments only make what is poor abilities still fail the too high expectations. Andy.