What was the point of destroying the Long Night of Solace and Ardent Prayer. Just to have an entire Covenant Fleet Arrive?

So during the Halo Reach Campaign after the mission Tip of The Spear you move onto the next where you take command of UNSC Sabres to take down a Covenant Corvette and destroy The Long Night of Solace and Ardent Prayer by Jorge sacrificing himself to Save Reach but then literally a few Seconds into the cutscene the Entire Covenant Fleet Arrives to Glass Reach. Like what was the point of it just to have a Covenant Fleet Exit Slip-Space.

Any thoughts? Because I'm curious about why the point of destroying the Long Night of Solace and Ardent Prayer, only to have a entire Covenant Fleet Arrive seconds later into the cutscene.