I suspect that those who want to argue would only stop arguing if you could indicate what creates a requirement for a CH system to have a ('dedicated') single point of isolation. As far as I am aware, BS7671 does not require anything (other than the installation as a whole) to have a single point of isolation, so you'd probably have to look elsewhere.If you consider that the FCU to a boiler is meant to be the single point of isolation for the central heating system which includes the boiler, ancillary wiring, pump, room thermostat etc - often wired in 0.75mm² or 1mm² then perhaps this argument can go away.
As I and others have said, it's all a bit moot, since I personally don't recall having seen any CH in recent times that was not supplied via by a BS1363 socket/plug or FCU (hence a BS1362 fuse). The argument has really all been about whether manufacturers should be 'requiring' something that at least some people regard as 'unnecessary' (even if it's virtually always done!).
Kind Regards, John