Cardassians are also nowhere near a superpower anymore and had billions die and their entire government was upended.Both the Klingon and Romulan fleets were decimated after the Dominion war (even moreso than the Federation), and it was predicted it would take decades for them to fully recover with only the Federation being a real power in the Quadrant in the meantime. By the time of this new series they may only be just starting to approach a level similar to what they had prior to the outbreak of the war.
Gowron's death and Martok becoming chancellor is a pretty big deal too.