MerchantVenturer,
You raise very interesting points in your post.
When FR had limited European routes and flew Dublin - Murcia as one of its earlier Spanish routes, it then launched Dublin - Alicante, ironically on the same days at the same times. I have no doubt this was a closely measured comparison and various stats measuring everything from sales to yield to no of customers checking the pricing to the level of ancillary services booked by passengers on respective was powerful data.
I'm not a Ryanair insider so I don't know for sure. Though I'd say the CWL TFS route will be very good exercise. If hypothetically the data shows that CWL is more attractive for holiday fliers (eg) then they may ultimately treat CWL as the secondary airport for BRS... Look shat is happening at Milan and Brussels. I can see CWL bring the secondary airport for BRS and a host if destinations being served that are not ex BRS , the idea to closely match BRS for this experiment on a similar route makes perfect sense ...