For what it's worth I'm certainly not advocating the banning of FL90 overflights within the TMA. Yes they do have a disproportionately high workload, and due to their weight are very unlikely to be paying route charges. BUT they are still a 'valued customer', they're often rerouted some way of their flight planned route to ease traffic flow and we would always have the option of saying 'no' if we're unable to accommodate.
This is very rare indeed but always possible. Or they can drop outisde CAS and trundle beneath!!