It leaked away because people didn't want the hassle of going to Manchester
Nonsense. It "leaked away" because the management at MAN were not bright enough to see that LO CO s would be able to both generate new traffic and leach business travellers. Had MAN offered easyJet and Ryanair deals at the turn of the century and a little before, Liverpool would now be struggling.
but because there was no need for such an airport in the North of England. The model was flawed.
Again nonsense. Have a look at the routes ex MAN in the period 1988 - 2001. A variety of factors - all well rehearsed here and elsewhere - have changed the picture regarding long haul and legacy carriers since then.
Your whole post smacks of uninformed isolationism. If easyJet and Ryanair were to vanish tomorrow, how long do you think Peel Holdings would carry on before building on the airfield?
Geomorphology and population centres in a small island favour certain metropolitan areas over others. Manchester has had, and continues to have, a greater economic gravitas than either Liverpool or Leeds.
Had Burtonwood not been undermined by the Lancashire coalfield, Manchester Airport would have been established there by around 1969. As it was, and is, the largest airport in the north of England is positioned on a site with excellent surface links, reasonably central to Liverpool, Leeds, Stoke and Preston/Blackburn and with land for further growth when the time comes.
As for condemning people to "gateway" via Heathrow, you obviously either enjoy "hell" or have little experience of connecting there.