I don't think many people thought they'd never be used - it's just that something half the cost might mean twice as many with much of the capability - as ever we spend 50% of the cost to get that 10% extra capability which is rarely needed
I was trying to make a general point, rather than one about the Type 45. Is the capability that you only need 10% of the time the ones needed in combat? In the case of a ship, things like measures to reduce the radar cross section, missile systems, decoys, radar.....
Likewise some seem to think that instead of Typhoon, we could have a cheaper aircraft with is slower, less agile, and has little or no air to air capability.....
The next conflict will be unlike Afghanistan, so our forces need to be able to survive in an environment where there are credible air or maritime threats.