Sorry but IFR ATM's and many VFR transits not calling are exactly the reasons why CAS should be established, if not will we ever see any more CAS established around developing airports? I don't know the Humberside story well enough to comment but each application for CAS is different, CVT will have a strong case.
"how long would Birmingham as a competitor put up with delays to their traffic caused by movements into Cov?"
Now switch it around, if CAS can help with the interaction of the unit's there should be less delays for both CVT and BHX traffic. Don't fear change, this is going to happen eventually....