The WCML has a lot of issues which the ECML does not. The amount of freight that still needs to be accommodated (and remain competitive) on that two-track section north of Carnforth, with the associated gradients, slower speeds and then much the same for Carlisle / Gretna Jn to Carstairs.
Add in, as the train approaches Glasgow, it is then a part of a very vibrant suburban rail network, whereas the same can't be said for the approaches to Edinburgh from the Dunbar direction.
You've also not got many major settlements of note north of Newcastle, save for those which can be relatively easily-served by two of the however many trains per hour that are operating. Morpeth - 500,000 journeys per year; Alnmouth 353,000; Berwick 630,000 and Dunbar 399,000. Newcastle being the 'break point' between London and Edinburgh, the comparable version on the WCML is Preston. With that, north of Preston you have Lancaster almost 2,000,000; Oxenholme 542,000 and an interchange for other key stations such as Kendal and Windermere; Penrith 610,000; Carlisle 2,100,000 and then Lockerbie and Motherwell, as well as a need to offer service to both Glasgow and Edinburgh.
You also have the problem of a lack of trains between places like Crewe and Preston, which is only hourly. Half the time, I seem to travel along that small axis and finds things are chaotic. And with the way the "Via Birmingham" service runs, its even got the issue of serving the Midlands, the Crewe interchange, and yield manages people onto it.
Decelerating the London to Glasgow 'direct' is not going to be popular, but it feels like adding a Crewe stop would make a massive difference. Or, you go fully-abstract. You run an all-day, half-hourly Avanti to Liverpool, and replace north of Crewe one London Midland path by diverting it to Preston. With a Hartford stop, it would also open up other links. You wouldn't have a changed frequency, but you could readily have an auxiliary Birmingham to Preston service, possibly formed of 8 coaches.
Or, you run the Avanti West Mids as a Liverpool via Birmingham, and 'recycle' the paths for the second Liverpool (e.g. stopping at Tamworth and Lichfield) as a second Scotland. Factoring in a Birmingham - Preston '350' service, and you could cause the existing London - Glasgow to be accelerated to be non-stop Preston, then Lancaster, then again non-stop Carlisle. If one from Liverpool / Manchester to Scotland is flighted immediately behind, people can jump ship at Preston / Lancaster for Oxenholme / Penrith with no obvious journey time penalty.