It's not just the flash duration or battery. With a focal plane curtain shutter, only part of the image is illuminated as the shutter travels across the image plane. With a leaf or diaphragm shutter, the whole image is exposed to the flash, which triggers when the shutter is generally fully open.
Originally Posted by mweintraub
If you're using a focal plane shutter, the results of shooting faster than synch are dark bands at one end or side of the image where the flash was not exposed. The faster the shutter, the larger the band. Based on your 1/200 showing underexposed, I would guess a flash synch of 1/30 on a focal plane shutter. The RB-67 uses the leaf shutter, so synch is possible at all speeds the lens can accommodate.