Isn't this your 'wanting it both ways at once' logic rearing its head again. Spend months (years?) moaning about centralisation of air services in one place and how the regions are missing out. In the next breath, regions suddenly becomes region and you are making the case for centralising the services of half the country in Manchester. Do the politicians and business leaders of Brum', Leeds, Liverpool... really want this, or are they just as proud of their own regional identities are you are of Manchester's and would actually want to see their own airports develop - arguably at the expense of MAN. I'm not starting a willy waving war here - just pointing out the contradication.
Quite frankly it's prop estrous to compare Manchester to Birmingham, Leeds, Liverpool etc, they are in the wrong location, they do not have the transport links and in some instances are limited by both demand and indeed capacity.
Based on major populations centres then yes for "half the country" Manchester is much more convenient.
Granted there will always be exceptions, of course there will be some niche services that will be successful but Manchester is the only credible platform that can support a wider range of LH services.
It is centrally located and can therefore attract passengers not just from Manchester, a massive provincial capital in its own right it can also attract pax from regions on the margins as well. It is the second most popular overseas inward destination outside London so the traffic is not just one way, that is another important factor. With three terminals and two runways and vast apron space, it has the infrastructure to cope.
The question is whether it can be made more "commercially attractive" in terms of fare structures etc and also whether it can break the perception of simply being classed as nothing more than a regional airport.