The Obsidian Order lost more than just 20 ship. Tain was systematically culling the Order to clear his way for his return to the top and these two events so close to each other would have gutted the organisation. The Cardassian military seemed more or less contained by the Federation and also in decline in stature and couple that with growing civil dissent you have a power that would have more worried about internal matters.
As for the Romulans, a culling there might have also gone about or maybe it was a long game and the Dominion was using the Tal Shiar to shift pieces in the Romulan Senate so that people like Vreenak would have the power when it mattered to keep the Romulans as isolated as possible. Plus in theory they are meant to be the "furthest" power from the wormhole and their position might negate the somewhat as a direct threat to a Dominion invasion.