BHX will never replicate the hugely expanded network at EDI as you rightly point out they are in different markets and locations in terms of other airports.
My point is that EDI have mostly managed to allow legacy and low cost to flourish alongside each other. So has MAN who were IMO even later than BHX to wake up to the need to attract loco carriers but have done so very successfully.
Their business models must be flexible enough to do so. BHX needs to adapt its business model likewise to grow (faced with such intense competition for pax from MAN, LTN and perhaps BRS) as like it or not, growth at most UK regional airports in the past decade has been mostly loco
BHX needs to further look at its cost base and become more commercially attractive to airlines across all spectrums to enhance its network and hence attractiveness to pax.