I shall post here in an effort to allow the LBA thread to get back to LBA business!
Leeds Approach talks at length about population being the key: So lets consider London.
Based on your argument long haul carriers would be happy to fly from LHR, LGW or STN as all have reasonably large catchment areas as well as drawing from Central London. The reality is that LHR is where the longhaul traffic migrates to whenever possible. OK, LHR is the hub airport for the UK but if it is all about population then following LA's mantra, surely the other 2 should support longhaul operations??? Both have catchment areas greater than 5 million. Yet, most of the LGW - US routes moved when Bermuda 2 ended & STN has never really supported a longhaul operation successfully. Many people from Cambridge / East Anglia area drive straight past STN to get to LHR in much the same way as Yorkshire folk drive past LBA to reach MAN. The airport at STN is not constrained as LBA is yet there is still little or no appetite from airlines to fly longhaul from there. (The same is true for the BHX catchment area although they do support some longhaul traffic.) Sadly that is why I think your argument on population may be a little flawed.
I accept that if we were starting with a blank piece of paper LBA would not be the first choice but we are where we are and I see no commercial, political or financial appetite for this.