That already is the case, isn't it, apart from the Liverpool-Norwich. Admittedly this train has a punctuality problem, but that isn't insurmountable.
Nope; Southport to Alderley Edge, Blackpool to Hazel Grove and Cleethorpes to Manchester Airport all use parts of the route. I'm fairly certain that Bolton to Stockport was built into the franchise so it'd be politically difficult to remove the connection. The fright takes the Style route anyway so actually already fits in that respect.
As @
Dspatula says, that's quite a few services per hour - four passenger trains per hour in each direction cross between the "Airport" lines and the "Stockport" lines (or vice versa).
Remove those and you could have a much smoother set of services at Piccadilly, effectively running as two stations (in the way that Clapham Junction sees lots of Victoria services and lots of Waterloo services without conflicts)
I wasn't sure if any of the freight came from the Stockport line, given the random nature of freight, so cheers for clarifying.
It's not even a branch, just one station call on a stub. If you could carry on through and connect with the other line at Ashley it wouldn't be so bad, but someone built an airport in the way...
In an ideal world, sure, it'd either have been a station on the line between Heald Green and Styal, or a through line onto the Mid Cheshire route - it could have been a huge benefit to regional connections (e.g. a through station on the Heald Green - Styall line could have meant lots of Piccadilly - Airport - Crewe services running that way (e.g. the Cardiff service and the London service stoping at the Airport)
However, given how things are, we have nine trains per hour from Piccadilly along the stub branch, eight of which terminate there (the other terminating at Crewe) the majority of which are non-stop between Piccadilly and the Airport, meaning the the local stations don't have a very good service - and can have quite a lop-sided service)
To ensure this, the nine services per hour are pretty badly timed (e.g. I think that - pre Covid - there was a seventeen minute gap in one direction, and a few times where three trains would run within a ten minute window) because the Airport services were tied to paths towards Glasgow/ Edinburgh/ Llandudno/ Cleethorpes etc.
So, given the realities of where we are, I think the only solution would be to simplify the type of services to the Airport, remove as many conflicts between "Stockport" and "Airport" as possible (making 13/14 much easier, since everything from 13 would be for the Airport and everyone for the Airport would go from 13).
Maybe the Airport services could continue through to a combination of Leeds (via Victoria)/ Preston/ Liverpool, but at least that would remove the messy situation we currently have (which is great for someone in Newcastle travelling to Manchester Airport once a year but comes at the cost of reliability across much of northern England)
I have thought whether there is any merit in combining the XC services to Manchester and a TPEX service say to Hull or Middlesborough. Whilst it would improve communications from North-East England to the Midlands and Cheshire-Yorkshire connections. There would be the problem of having to miss out either Manchester Airport or Stockport on the route. That said, another Leeds to Birmingham service might be useful in tackling overcrowding, but I am not sure what the time difference would be with going via Sheffield.
Leeds - Birmingham is more like two and a half to three hours (via Manchester) depending on connection = compared to the current two hours (via Sheffield), but that takes the slow slog round Manchester into account.
Whilst HS2 should slash the Leeds - Birmingham times, I could see some merit in extending the XC services to Leeds etc, providing a number of through links (Stoke to the ECML, Huddersfield to the WCML), it has some merit