It is not so diagonal that it actually is worth much in flight deck length though IMO: the clearances around the rotor remain much the same. So yeah, I would look at the british Type 45 destroyer for flight deck size.
Very true, on something like the CH-46 (and in the same vein the CH-47) with two rotors the advantages are limited. It works on the Burkes because the flight deck is right at the back, but with this arrangement it doesn't work as well (especially with the ships that have the Mk-26). The angled approach is more useful with a smaller rotor area but something else that extends past it like a tail rotor. So useful with squeezing in a SH-60 or even a CH-53, but not really a CH-46, so larger flight deck it is!