Are you 100% certain it's the Executor in that opening shot? I always interpreted it as look at how massive the bottom of this bridge section is, then cut to the entire star destroyer to show the scale of the rest of the ship which is then engulfed in the shadow of an even bigger ship that dwarfs the already massive star destroyer in size. The whole thing being a play on the opening of the original Star Wars.
Always though so myself. For that ship will always be a regular star destroyer that gets dwarfed by the shadow of the Executor...
I have to agree with everyone here Ady, it makes more sense to have that bridge be for the SD as its saying to the audience look how big and domineering I am, only for it to be dwarfed by Vader's ship moments later