One cannot argue with the basic principle that BHX is better positioned than LHR to be the country’s major hub. It is after all geographically central - simple as that.
However there are significant practicalities that have to be faced:
1. Though excellently positioned for the motorway network, that network is already close to capacity in rush hour.
2. The NEC is too close. Major exhibitions would seriously impact an expanded BHX (they already do!).
3. The rail links needs sorting out. Direct trains from London yes. But a large proportion of the local Midlands catchment have to change in the hole that is Birmingham New Street.
and the biggy
4. Once a hub like LHR is already established it becomes self-sustaining unless there is some massive incentive to change (whether governmental or entrepreneurial)