Truth be told, I never found Klingons realistic. It's simply impossible to develop a civilization with such aggressiveness. Sure, an alien species may have different advantages, but we don't see other advantages, they are simply: human but aggressive. e.g. Vulcans are 100 times more intelligently depicted: They are shown to have been trying to repress feelings but at the same time there is a backstory that makes perfect sence: their physiology makes it easy to explode emotionally so some emotion-repressing meditation is constantly needed, makes sense. Klingons, what are they, humans from the dark ages. They have nothing other than being aggressive, humans with a problem. Realism and logic suggests they are a fairy tale, they would not have developed beyond caves with such aggressiveness, how are they even going to develop groups for a common purpose with such hate and destructive tendencies. Unless they stole it all.
A starship board game called Star Fleet Battles was created in the '80s based upon TOS. In that game the crewman of the Klingon ships are alien slaves kept under Klingon control. The Klingons command and do the fighting. I always wondered if we would see that in Star Trek sometime.