I think one of the few things that Trek has gotten consistently and traditionally right is that ship-board energy weapons have observable travel times. It's the scale of the ships that's off. At the relativistic distances at which starships encounter each other, a beam's travel time would be short but observable. Keep in mind that one light-second is only 186,000 miles, give-or-take — that's only about 5/6 the distance from the Earth to the Moon. Cosmologically speaking, any two starships seen together on screen would basically have to occupy the same space in order to see comparative sizes we see on screen.