They're both lackluster compared to the competition.
Truthfully, it's an apples and oranges comparison. The Y&B was built in 1990, and even the rooms have been refreshed and modernized a couple of times since then, but there are limitations as to what these updates can do. When it was built however, compared to the off-property competition it was significantly nicer, however since then the completion has stepped up its game with its offerings.
Gran Destino is a brand new resort, as such it should be compared to one. The biggest critique of the rooms and decor is not that it's without theming, it is that what is in the room is generic. Newer non-Disney deluxe hotels have so stepped up their game, that they're bringing a better product to guests. That better product makes Disney's seem ordinary.