And again I will ask: Where is Starfleet's presence on DS9, other than the few officers we saw on the station? If the Defiant was on a mission, why aren't there any backup ships? What happens if the Dominion suddenly decided they were going to send an attack fleet through the wormhole?
Again, we go back to the whole nostalgia. They're trying to mimic early years DS9 episodes, or at least pre-war episodes. You'll note there aren't any ships at the station at all besides the Cerritos and the Karemma ship, just like DS9's first four seasons where you only see ships which have a specific purpose to the episode's story docked at the station. Hell, back then it wasn't uncommon to show a shot of the station without the Defiant docked, but then in the next scene the characters mention the Defiant being docked. The busy station stock shots where there's always a ship docked or flying by didn't start until the fifth season, and indeed that's also when we started getting more consistent about having the Defiant visibly docked at the station on a regular basis.
This episode was about nostalgically recreating the DS9 feel more than it was presenting a realistic depiction of Starfleet's presence in the Bajor sector. I mean, hell, the start of the episode when the Cerritos arrives at the station they play the version of the DS9 theme from the first three seasons as opposed to the one from seasons 4-7, making it damn clear they're intentionally trying to evoke the first half of DS9. Indeed, the sudden arrival of a Dominion attack fleet was a concern on DS9 starting in the third season, yet throughout the entire third, fourth and first half of the fifth we see the Defiant off on all sorts of missions, leaving no Starfleet presence at the station at all should the Dominion come knocking. You can't condemn Lower Decks for making the same oversight DS9 made all the time, especially since Lower Decks is specifically and intentionally mimicking DS9 in this respect.
(Full disclosure: I fully realize that I am taking this way too seriously. This is an animated comedy show that doesn't take things seriously, so why should I? Well...because I'm a realist, and this show isn't really all that realistic.)
That's just it. We're in the third season and the show's format is well known by now. It's a nostalgic comedy which doesn't take itself seriously. At this point, why does anyone expect otherwise?
And really, when has Star Trek ever been particularly realistic?