Whilst I agree with the points to some degree, that isn't always the case. Using Cardiff as an example again, there is a lot of leakage to Bristol, mainly because people default to Easyjet and Ryanair.
Its also been commented that some holiday websites aren't selling holidays using Wizz.
Similarly there is a huge push with South Wales Travel Agents for the new Jet2 holidays from Bristol, with little push for using CWLs Airlines for holidays, such as TUI, Vueling and more recently Wizz.
So I do think brand awareness is needed in some cases as people may not even think to search for flights from Cardiff and automatically type in Bristol when searching. I'm sure DSA may be in a similar situation with MAN, EMA and LBA not too far away.