It's more than simply "human" expressions. I for one, wouldn't know about John Masefield, if Spock hadn't corrected Leonard McCoy on the subject. I doubt many French people know of him, or American for that matter.What I found surprising is Quark quoting earth poetry as in Little Green Men when he says: "All I want is a tall ship... with a load of contrabande to fill her with." Why would a Ferengi know about that poem? He also says in that episode that humans from the 20th century are people that he can relate too. Confirming that Quark is much closer to modern day humans than anyone else on the show.
Aliens quoting human expressions is, as you Ferengi say, a tube grub in a waterfall.
It makes it very surprising that a Ferengi would know him so well that he would use him so casually.
Not to derail the thread at all, but the idea of a Ferengi knowing Earth poetry is actually more in line with their culture than Klingons knowing Shakespeare. Ferengi were categorized as "Yankee Traders" who would seek how new opportunities of profit from foreign lands. The idea that Quark would learn how to quote human sentiments would certainly be in line with trying to appear to be sympathetic and open to Earth culture.
Or, it could be that Quark has heard so many humans talking in his bar that he just picked up the pieces that appealed to him.
As for Dukat, I always found him and Sisko to be the more interesting dynamic in the show. How Dukat is constantly living in his shadow, to the point that he must take on the opposite side to Sisko, even in the Bajoran religion. While I think he becomes more 1-dimensional as the Pah-Wraith bad guy, I think it reflects his downward slide in terms of power, going from government official, to religious power monger. Regardless of your views on religion, using another person's religious beliefs to further your own personal power is the act of a con man not that of a powerful leader.
It is a sad end for Dukat.