This is one of the many frustrating aspects of STD.
This season has 13 episodes. We are 4 episodes in and after the biggest status quo change in the history of Star Trek, nobody in the show is talking about the current state of the galaxy besides "Starfleet/Federation is gone". And this information we have been told in slightly different iterations three times in a row in the first three episodes.
What happened to the Klingons/Romulans/Cardassians?
Who are the major powers in the A/B quadrant? Who filled the power vacuum after the Fed was gone?
Why didn't the Borg/Dominion move in?
Are there new superpowers or are warlords/pirates/crime syndicates/courier organizations in charge?
I hope with today's show (E5) this will change, and we get some information about the state of the galaxy.
You're forgetting that this crew is from 2258. A list of items here:
1) They've never interacted with the Romulans. The Earth/Romulan War was about 100 years ago, from their perspective. And "Balance of Terror" (TOS) won't happen until eight years after they left the 23rd Century.
2) Even if they know about the Cardassians, they hadn't had any Border Wars yet.
3) The Discovery crew have no idea who the Borg or Dominion are. The story is being told from this crew's point of view.
4) Communication is limited in range and warp itself is limited in range. Sahil explained this in "That Hope Is You". Any Major Enemy is going to be limited too, if they're affected by The Burn.
5) The Borg are the domain of
Picard. I'm assuming the writers of
Discovery don't want to step on the toes of
Picard. Who knows what PIC wants to do with the Borg? For all we know, they may want to change the Borg into something else. If they were to reveal this in DSC, or the ultimate fate of the Borg in general, that would be potentially spoiling PIC's ending; if it were to focus on the Borg. I want
Picard's options to be open, not shut.
6) How do we know if the Dominion are still around? And to do you one better: How do we know that Odo didn't reform them when he rejoined the Link? That's what I was under the impression he was going to do. And with Rene Auberjonious having passed away, the door is closed on Odo returning. Even if they do anything with DS9 in the future, I think we'll never see him again. So I'd like to think the Great Link is where he stayed for good, to do some good.