I can't see APD having that much of a major effect on BRS and jobs in the area.
If anything it will stem the expansion flow it's seen over recent years, evening things out between BRS and CWL. By no means should any Airport have any right over it's passengers that live in the catchment, but it would certainly help CWL compete for Welsh travellers that actually want to fly from their local Airport. CWL will never reach the levels of BRS
It's also not all about BRS. It could win back passengers from London and Birmingham