The big difference is that RRL was designed for 2 track pairs
It is a massive amount of infrastructure to quad the Werribee corridor. Almost every station would need modifications or a complete rebuild to accommodate the track pair. Reconfiguration of serval Road overpasses and the removal of every LX. That before we even get to Newport.
RRL has been designed to accommodate the additional track pair. Which will be built next to exisiting stations. Deer Park and Adeer will need to be rebuilt, that being a good thing. They barley classify as stations as they are now. Modifications to the M80 underpass to remove the LX and the removal of the other two LX.
With work already underway on the Ballarat corridor this is where Geelong services will run now and into the future.