I'm just trying to be optimistic with this post and not just take the P (make's a change).
I suppose that an air defence destroyer without the 'air defence' capability actually returns the T45's to the RN core role of Frigate - and a heavy frigate at that.
By 'Frigate' - I don't mean the cold war ASW version, but more a Nelson - Aubrey type of independent duty warship to show a strategic presence around the world.
The ships will not be useless per se - they will have uses; just not in the core role that they were ordered for (and let's hope we never need - and hence miss - the key capability) and then paid for at twice the price.
I'm not sure what ASuW they have other than the big gun on the front...