I never understood the "tribal warriors in starships" cliche of space opera.
Given how oppressive the Klingon Empire must be to the non-Klingons they rule, wouldn't a protracted war decimate the Klingon population because they can't count on their slaves fighting for them ?
Firepower based warfare with its emphasis on mass, regimentation, and efficiency renders warrior value systems obsolete. So logically the entire religion of Kahless would have fallen apart with the development of firearms and the Klingon Industrial Revolution. Unless, of course, like the Japanese a Klingon warrior society got a Lot of high tech from somebody else very quickly without having to acquire modern values. I read some Star Trek fiction that postulated that some more advanced race was impressed with Klingon warrior ferocity and gave them a lot of high tech in the expectation that they would be their pit bulls in starships. Big mistake.