As previously stated, I thought ME's animations were feed for innovation. One reason clearly seen for the transfer distance is the fact that the two weights/wheels are counter rotating in relation to each other. The slightest infinitesimal difference in connective measurements would be like throwing a monkey wrench into the works.You are right, both sides should alternate in speed-up.
The left one is simply constant in rotation: thus the same transfer-difference is put on the other side.
This brings forth an image of a steam locomotive where the drivers are attempting to rotate in opposite direction. If you do your browsing research as I do, you soon find yourself learning the history, usage and concepts of what is known as the "Johnson Bar" employed in steam engines.
Ralph