The Dominion got fooled time and time again by Sisko and his crew.
That's normal villain decay after using them so much.
Remember how it seemed impossible to destroy even one Dominion ship in their first space battle? By the series finale, the Defiant was destroying multiple Dominion ships with ease.
True but it seems like the Dominion's dealings was based on dealing with scared or easily coerced cultures.
Weyoun had a Cardassian city destroyed and killed millions of Cardassians, and then later expected them to forget about it and go back to working with the Dominion as if nothing happened.
It was almost as if they were used to getting a certain response like that after all those years of dealing with GQ cultures.
Maybe that's how some GQ cultures evolved, or developed after the Dominion took over most of it.
I remember when the Founders decided to start breeding a new strand of Jem Hadar especially for the Alpha Quadrant.
It was said that their 'psychological profiles" were designed for combat in the Alpha Quadrant.