If they have instantaneous subspace communications over light years, surely they could set up an array of telescopes which communicated their data via subspace?
We can find any in-universe coherent solution, but it's not our responsibility. The authors setup the scene like turn on a lightbulb near a star, and after a second a bunch of ships, previously scattered around the galaxy, appears. Not even the time to react to the signal, communicate to the captain, startup the engine, and travel.
In the same episode, Mary Sue piloted a federation suit inside an incredibly dense system wide asteroid field, btw a forced but cool moment. They made the error of specifying the distance and the time needed, I don't remember the details, but the resulting speed was unholy. If it needed to accelerate and decelerate, top speed was even higher.
They just throw around stuff and cool visuals in a brain crushing mix.
At some point, Mary Sue organized a trap for future self, and nobody had the notion that future Mary Sue known about the trap that she setup, and come prepared for it.
I feel ashamed that I watched it all -_-