A point you have raised i find considerably interesting.

With regards to the destruction of Alderaan from within the view screen.

Although when you consider the explosion has a big jump cut in it. This may actually explain why there is a jump cut if the destruction was to be spread across 2 or 3 shots.

Perhaps the Laser forms the cone we then see the planet hit through the viewscreen being hit and the start of the explosion

Next would be a short reaction from Leia. Then cut to Space to complete the explosion.

So although we are merely talking about half a second or so.

I think it is the answer to the Jump cut.

Also it might go the other way around Space explosion. Leia reaction. Remainder of explosion completes in the view screen.

I might have a go at that. Where can I find the reaction shot?