Hi
When people ask ‘why do my lovely sharp graphics look great in the Viewer, but horrible in the Canvas’ the answer people get here is that the Viewer is a QuickTime-engine’s display window, whilst the timeline and Canvas are working with the FCP display-engine, on top of FCP’s editing-ready code-base.
Furthermore when you enable Real-time playback for the timeline, FCP reads-ahead the timeline and buffers the playback to the Canvas to allow the real-time to happen. Only it’s not quite real-time, there’s a slight buffering latency.
It’s that slight timeline read-ahead buffering that gives the slightly sticky scrubbing, I would guess…