About the strength of the dominion:
The last strategy of the dominion was to retreat behind the cardassian borders, increase jem'hadar/ship production, and, in ~2 years, when ready, to attack the federation/klingon/romulan alliance.
Sisko's words for what would happen then were ~'God help us'.
The dominion expeditionary force, in a mere 2 years, by using only cardassian resources, can become more than a match for the federation, klingons and romulans combined.
What about the dominion proper - in 2000 years, by using the vastly larger resources of the gamma quadrant dominion?
The federation, klingons and romulans are outmatched, by far.