Hmmm, the only thing I can think of right now for highlighting the cannons is to reintegrate the attack on Kijimi, but cut before we see the planet erupting. Palpatine says to “let it [a world they know] burn,” and we see this new cannon is strong enough to crack mountains and raze a city, but by dramatically cutting away to a different scene after the close-up I don’t think a new viewer would necessarily assume the planet exploded.

Downsides:

The “conjuring” line is still there, so adding back the laser, a viewer might think even more that these are all new ships
Without cutting to a reaction by the heroes, there might not be enough closure and the audience might spend the rest of the movie waiting for us to go back to Kijimj. But of course we can’t have the theatrical reaction as is, because it’s the most attrocious series of forced exposition in the movie which also specifically states that they blew up the world. It would have to be either a very heavily edited version. Maybe… during the last few seconds of the destruction visual, the audio transitions to Poe’s voice mentioning the planet was attacked in a vaguer sense, and then when the visual cuts we’re at the scene with Poe and Leia, as if he’s talking to himself to her.