But you can't change geography ... As an example expecting somebody who lives in Taunton to take a flight from CWL might be comparable to expecting somebody who lives in Ayr to take a flight from CAL.
Not exactly sure what that means. Where's CAL? CWL is much closer to Taunton than BHX/LHR/LGW. Not every person from the Southwest flies from Bristol.
And the right carries with the right routes and the right schedule is already in the market. At Bristol.
They are indeed, currently, only specific short haul and charter long haul markets. But they aren't the only carriers around. Look at how Vueling has filled the gap.
QR is prime example of a market filler that isn't in Bristol.
There are other carriers around that would attract people from using other Airports (Not just BRS)