Well, sure, in your version you made them concubines, but in the post made by the author they are described as wenches. And the author hasn't posted a revision or responded directly to your feedback so maybe he/she worked out that detail and doesn't plan to change it.
To be honest, when I first read the concept I thought it was a drama, comedy didn't even cross my mind. That may be because of my personal taste but still the original logline, and even your version don't paint a picture of comedy in my head.
I did list specific examples, and it doesn't necessarily need that I do think some a little more specific than "compete" or "vie" could help. Nir Shelter's version more so paints a comedic picture in my mind. "Sabotage each others' attempts" sounds like the type of situation a?comedy would present.
Even your description, "They start out as co-conspirators who want to kill the king, then turn into rivals trying to kill each other (eventually) as they fight to win his favor." doesn't paint a comedic situation to me. Not to say I immediately see a super-dark movie, but I don't exactly see them cracking jokes or pulling off silly hijinks.
But that does bring up the question of what kind of tone, what kind of comedy?
Just my thoughts.