As it stands, my reckoning is that both brakes are not getting the maximum leverage that can be applied. The front hub lever is at 90 degrees to the cable, applying the brake as it is reduces the effective radius and therefore leverage.. Try turning the lever over, the lever may then point a little further downwards. You want it just before 90 with the brake on.
The rear brake lever on the cross shaft can be moved backwards on the splines. One of the problems encountered is the incorrect length of aftermarket rear cables, or the wrong one for the model year. BSA messed with that rear brake over the years. Both levers need to be set before the magic 90 degrees at rest.
Plenty for you to find already on the Forum. Don't expect miracles, the full width cast iron hub is rated as just about adequate, even when well set up.
Villiers Services, Brierley Hill, West Midlands offer a well respected brake reline service, but as always, pays to check you have the correct shoes fitted, and fitted correctly.
Swarfy.
PS Came off a loaned Honda CB 72 mistaking gear lever for left side rear brake pedal. Front brake locked up on gravel. Stepped off as it slid along....
