I checked with the internal teams who relayed that the legacy channels have limited processing power while the X1 channels have improved components and can provide variable speeds during pipetting to better accommodate multi-segmented containers.
The legacy channels have a fixed speed. If the liquid to be transferred is in two segments of the container, then an average speed is calculated that suits for both segments. This is sufficient for many use cases, but is now further optimized with the new X1 channels.