That "the Dominion" lost is already ample proof that the Dominion would win all other wars hands down. After all, it only barely lost this one without hands, feet, head or half the torso! You aren't entitled to misusing the concept of "the Dominion" as applying to a tiny beachhead force when the point of the discussion is a rematch between the actual Dominion and the Federation (and hopefully a few allies on the UFP side again).
Nor have I misused it, Timo. Whether one is talking about the entirety of a government's military or merely a small fraction of it, it's perfectly acceptable to refer to said power by name in describing a sequence of events relevant to a war scenario. The Dominion may have sent only a small number of their vessels into the Alpha Quadrant, but that doesn't change the reality that they were defeated by the Federation.
I don't mean to imply that the same result would occur were they able to use their entire fleet from the Gamma Quadrant (and I haven't despite what a few others insist on believing), but it's not appropriate to argue that the Dominion wasn't really
the Dominion because they didn't have enough ships. That they underestimated the Federation (and its allies) is no fault of Starfleet's. It's merely a reflection of the Founders' overconfidence.