That's making an incorrect cultural-equivalency comparison, though, assuming that the Klingon system of jurisprudence is precisely identical in all respects to Starfleet's. When we've seen numerous onscreen examples over the decades (well beyond even TUC) showing that it definitely isn't.No, totally different circumstances I'm afraid.
Cpt. Louvois explains to Picard that Riker must act in the prosecution role given the remot nature of Starbase 173 and not having a staff. Regulations dictate that The duty falls to him.
I highly doubt that there was a lack of skilled legal professionals on Kronos, the Klingon Homeworld, who could have been called upon to prosecute over Kirk and McCoy. Professionals who weren't also caught up in performing as the Chief-Of -Staff for a newly appointed High Chancellor during one of the greatest crisis in the history of the empire.
I'm sorry, you can love Trek VI all you want, but it's a plot point that makes absolutely no logical sense no matter what way you turn it over in your mind. If you put it into any real world context, it is as inane and foolish as the Enterprise having 78 decks. Maybe even more inane and foolish.
Why does General Chang stepping into the role of prosecutor have to have an exact counterpart in the Federation legal system for it to suddenly make story-sense? The Klingon Empire isn't the Federation, and shouldn't be expected to adhere to the same identical cultural and political characteristics.