I think your rationale makes sense and on the 'right' track, ie already owned a 16.29, mono -pusher and looking for a white dial.
In the past, i much prefer the 16.29 larger movement and finishing but now that I get to understand better these Villeret movement from MB, so I think the 13.21 is as good. The pusher at 2 o clock kind of confirms the white enamel dial as the best choice. What sweet dilemma Nico! let us know your decision . All the best my friend !