DSA is relatively central, and could by your theory flourish should LBA close in favour of one airport. So why not focus growth in DSA?
The location is utterly critical to the predicted demand. It is to do with West Yorkshire urban area, the importance of Leeds City region but more important main arterial motorway and main rail (including HS2/3) connection. Would LCR be happy for DSA to be its airport when it has an airport that is admittedly less than ideal? 8 million people at the other end of a railway line is rich pickings even if you take just 2% of it.