Without comedy episodes DS9 would have been monotonous. I don't need a full 26 episode season focusing on just the war. What we got of the Dominion war was enough.
Hardly a ringing endorsement. No, but it was exemplary, and as such, it shows how quickly the constant attention to fighting only would become unbelievable. There were, of course, espionage/undercover stories, which focused on Kira, Odo and Garak. OTOH, the O'Brien story, Honor Among Thieves, has largely been lost over time despite some strong acting..
That depends. How funny are the one-liners? Seriously, I don't remember feeling that we weren't getting enough eps about the Dominion War. And there's no guarantee that yet another ep about a top-secret military mission would be more entertaining than, say, "Little Green Men" or "Our Man Bashir" I tend to resist the idea that "serious" is innately superior to "silly." Comedy and drama have equal value in my book.
I like Magnificent Ferengi and Who Mourns For Morn, but I agree some of the Ferengi comedy episodes are just plain terrible. In comedy episodes the Ferengi often get written like cartoon characters and it often crosses the line of being insulting to the viewer. But why shouldn't there be comic relief? After a series of heavy war episodes, a change of pace is totally welcome.