I think we are beginning to see why there is a problem!
ATC who 'own' the airspace and must regulate everything that happens within it. (Yes I know about the rules, my point is about the mindset). Zones which are considered 'small' (well they have to be otherwise in the SE there would just be one!).
And yet I can meander down the Manchester low level corridor with none of that happening. And that works (granted it would help if it were a bit wider and higher! and most of that class D is very empty).
Corridors work because they do not require you to do all the things you call 'service' and because of which you refuse entry into CAS.
As far as VFR traffic is concerned CAS should be patterned much more like a MATZ than the present vast expanses, through which virtually none of your IFR traffic actually flies. (I'm thinking here about less than 3000').
I'm not trying to pick a fight or goad anyone, but the whole concept that public access to huge chunks of airspace is governed by whether the people accessing that space pay for a 'service' is one which is by international laws illegal. There is a right of free navigation. Now if the 'service provider' puts restrictions on the access and the people who work for them keep on using the 'safety' argument do not be surprised when there is some pushback.
In the SE and other places transiting CAS is difficult. Controller workload is certainly a big issue and one which is usually sighted, but there seem to be no initatives to adapt procedures and arrangements, it's just the 'we're big, you're small' argument. If VFR traffic start logging Class D transit refusals then the size of the issue can be seen. Could the answer be as simple as having a single VFR frequency and controller at peak periods?