Though the Gamblers lack feats, the implication of their power was quite huge; it was stated that destroying the earth would be like destroying a virus for them, they were also called "omnipotent", and they actually managed to set a track spanning from the dawn of time (the actual big bang) to the end of the universe when it implodes into nothingness.
Still, the Watchers' feats are better (like affecting all reality as a side-effect of a fight between 2, and turning a whole universe into a pocket one for Uatu to contain within himself).
But considering that the Gamblers never showed any sign of weakness or hints of how to defeat them, it's only a speculation to say that the Watchers would destroy them (though they have the better feats).
I forgot about that scene, thanks for bringing it to my attention.
And considering that (now that i re-looked at the scene), Flash's statement about how the gamblers "would wipe out the world as casually as they would a virus" was exactly 1 page after your scan.......yeah, definitely not a hyperbole.