I think the bigger issue is that not thinking through the tech that's already been established (i.e., transwarp, transwarp networks, etc.), and writing it to work within that continuity, plays into the idea of how some of these ideas are thought out for the larger plot.
I mean it doesn't take much in the writing to establish that by the 32nd century those technologies exist, Starfleet (and the other powers use them), but the lost spore drive technology has an advantage in that it's 1) quicker to get where you need to go, 2) it's more ecologically sustainable especially after the scarcity of "The Burn", and 3) the spore drive theoretically gives the option of crossing to other galaxies, the far reaches of our universe, or entirely different universes.
I mean I've actually been surprised that they didn't base an entire season around a sort of "five-year mission," where Discovery attempted a jump to a distant galaxy, and went on a mission of ... well, discovery. Instead, the spore drive is used as basically to move the plot of normal (Trek) stories without having to acknowledge the passage of time from warp drive.
But for the sake of argument, let's go with the particulars the show set up from season 3. "The Burn" occurred. The Federation and the galaxy at large were still dependent on dilithium for warp drive. The scarcity of dilithium after "The Burn" meant the collapse of most of civilization, and the Star Trek universe went sort of Mad Max with groups fighting for dilithium the way post-apocalyptic Australian road gangs stole and pillaged for gasoline.
Fine.
But if you have that as a backstory, how exactly did the Breen build dreadnaughts? If we're going to go with the idea that everyone lived in a dark age where all of the major powers were near collapse because there was no dilithium, or alternatives to dilithium, and the Emerald Chain had near exhausted their ability to pillage it, how can the Breen possibly be a threat to a Federation that's in control of the one major resource the galaxy needs?
Why is Starfleet afraid of antagonizing the Breen when, from what we've been presented, the Federation controls the only (known) major source of dilithium left in the galaxy? The Breen should be the ones afraid. The only reason they're not is because the plot nees them to be a threat. Also, if Starfleet and the Federation are so scared of standing up to one faction of the Breen, what does that say about their ability to protecting member worlds?