I am being a bit soft in the head, or it that half hourly TP service pretty much what it is now, save a couple of extra services in the morning & afternoon peaks. And the same major destinations like Huddersfield & Leeds to the east will still be served, just with slightly different calling patterns and revised timings? Because if so you have to wonder just what the Stalybridge based poster is annoyed about?
As a fairly regular user of the North TP, and from purely anecdotal observations of course, but the flows from Stalybridge seem much heavier to and from Manchester than eastwards, much heavier.
I agree with all of your points.
The problem that we have on here is that some people seem to feel that, because a service links two points that there is significant demand between those points.
For example, I don't think that there's any particular reason for the Newcastle/Middlesbrough/Scarborough/Hull services to service Manchester Airport instead of Liverpool, or for them to serve Liverpool instead of Manchester Airport. It's just that these are the eastern/western branches of the TPE network, rather than any particularly significant number of Scousers going on holiday to Scarborough (for example).
(same applies to every other network of services, e.g. the number of Metrolink passengers from Altrincham wanting to travel all the way to Bury/ Rochdale will be tiny so I wouldn't lose much sleep if the northern termini were swapped, as long as these places retained their frequent service into central Manchester - in fact you could argue that Stalybridge is lucky to retain long distance heavy rail services when other local stations in Greater Manchester are now only served by tram)
For every hundred passengers at Stalybridge, I'd estimate maybe 80% head towards Manchester and of the remaining 20% the majority of them go no further than Huddersfield/ Leeds.
There's probably a token amount of people who'd like a direct service from Stalybridge to Newcastle, but then there are probably some people who'd like a direct service from Stalybridge to Bradford/ Wakefield etc.
Can't meet every esoteric demand, especially not in the days of simple clockface timetables (albeit with good connections at places like Huddersfield) - we shouldn't have the tail wagging the dog.