Southport line commuters had a regular service to Bolton, Oxford Rd, Piccadilly and the Airport (and prior to that, Stockport and beyond) which they lost, and in an underhand way, last May. They are left with a slower service via Atherton to North Manchester apart from a few trains per day.
Changing at Salford Crescent to get to Oxford Rd is only viable if you can guarantee actually being able to board the train you are changing to, which you can't, and the same applies with Metrolink - they are rammed solid at Victoria, and even if one can squeeze on the tram there, to get to the same place (say Oxford Rd) takes at least 20 minutes longer than the direct train they were used to.
Recasting the service through from Southport to Alderley Edge via Bolton would be the most sensible short term solution to both capacity and stock use and I believe that gauging work was done on the Southport line earlier this year with this in mind.
The intent to route all Southport trains via Atherton to Victoria from May 2018 was hardly a secret. The North West Electrification Programme was launched in 2014 and always included electrification of Lostock to Wigan North Western in its scope. This involved the services to Wigan via Bolton terminating at North Western and originating on electrified lines, in order to make best use of the wires. When Lostock to Wigan electrification was postponed, just enough 319 to 769 conversions were ordered to enable 769 operation of Wigan NW to Alderley Edge and Stalybridge services until the wiring is eventually completed. Extension of Alderley Edge services to Southport requires some diagrams to remain DMU worked, under the wires all the way from Bolton to Alderley Edge.
The Southport to Leeds services take 31 minutes from Wallgate to Salford Crescent via Atherton. The peak Southport to Alderley Edge via Bolton services take exactly the same time, so the Bolton route is not quicker.
The peak Alderley Edge service then takes a further 10 minutes from Salford Crescent to Oxford Road and 15 minutes to Piccadilly, versus only 3 minutes to Salford Central and 8 minutes to Victoria for the following Leeds service.
Google Maps gives the walking time from Victoria station to Piccadilly station as 19 minutes, to Oxford Road station 20 minutes. That is at a leisurely walking pace. I can do it several minutes quicker, despite my advancing years. For any workplace that is not actually inside one of the stations, the difference in walking time (time from Victoria minus time from Piccadilly/Oxford Road) would be at least a couple of minutes less.
So even for the absolute worst case of a workplace immediately south of Oxford Road station, the total saving in journey time (train plus walk) is no more than 15 minutes. For a workplace in the Piccadilly area it would be 10 minutes or less.
The employment area around Spinningfields is closer to Salford Central than to Oxford Road. Southport commuters who work here would have a significantly shorter journey time if their train went to Victoria.