Not quite right Stone
If the synch doesn't match, and the leaf shutter is only part way open when the flash goes off, the film is evenly exposed, but the shutter will perform like a second aperture and potentially reduce the brightness of the light that hits the film.
Sort of the same effect as changing from f/5.6 to f/11.
And the Mamiya 645 line cameras have focal plane shutters. There are a couple of specialized leaf shutter lenses you can use with them, but most of the systems lenses don't have a shutter.